Optimization of ranging sessions initiated by vehicle and pedestrian UES

ABSTRACT

A responder user equipment (UE) in separate ranging sessions may determine whether there is a collision between the ranging signals assigned to broadcast in the separate ranging sessions. A collision in the ranging signals is detected when the ranging signals have the same frequencies and broadcast times, e.g., the broadcast time of one ranging signal is within a predetermined amount of time for the other ranging signal. When a collision in the ranging signals is detected, the responder UE sends a message to the initiator UE indicating the possibility of a collision. Available times for broadcasting the ranging signals may be determined, e.g., by the responder UE or the initiator UE. The initiator UE may initiate a new ranging session based on the available times for broadcasting the ranging signal or may proceed with the ranging session with the possibility that the responder UE will not participate.

BACKGROUND Background Field

The subject matter disclosed herein relates to wireless communicationssystems, and more particularly to methods and apparatuses for ranging orpositioning of user equipment in a distributed wireless communicationssystem.

Relevant Background

Obtaining accurate position information for user equipment, such ascellular telephones or other wireless communication devices, is becomingprevalent in the communications industry. For example, obtaining highlyaccurate locations of vehicles or pedestrians is essential forautonomous vehicle driving and pedestrian safety applications.

A common means to determine the location of a device is to use asatellite positioning system (SPS), such as the well-known GlobalPositioning Satellite (GPS) system or Global Navigation Satellite System(GNSS), which employ a number of satellites that are in orbit around theEarth. In certain scenarios, however, location determination signalsfrom an SPS may be unreliable or unavailable, e.g., during adverseweather conditions or in areas with poor satellite signal reception suchas tunnels or parking complexes. Moreover, position informationgenerated using SPS is prone to imprecision. For example, off-the-shelfGPS positioning devices have an accuracy of a few meters, which is notoptimal to ensure safe autonomous driving and navigation.

Coordinated or automated driving requires communications betweenvehicles, which may be direct or indirect, e.g., via an infrastructurecomponent such as a roadside unit (RSU). For vehicle safetyapplications, both positioning and ranging are important. For example,vehicle user equipments (UEs) may perform positioning and ranging usingsidelink signaling, e.g., broadcasting ranging signals for other vehicleUEs or pedestrian UEs to determine the relative location of thetransmitter. An accurate and timely knowledge of the relative locationsor ranges to nearby vehicles, enables automated vehicles to safelymaneuver and negotiate traffic conditions. Round trip time (RTT), forexample, is a technique commonly used for determining a range betweentransmitters. RTT is a two-way messaging technique in which the timebetween sending a ranging signal from a first device to receiving anacknowledgement (e.g., in the form of return ranging signal) from asecond device (minus processing delays) corresponds to the distance(range) between the two devices.

Ranging sessions in a distributed system, i.e., without infrastructuresupport to coordinate messaging, may result in multiple ranging sessionsoccurring simultaneously that may include overlapping sets ofparticipating UEs. For example, multiple initiator UEs may initiateseparate ranging sessions with the same responder UE, which may resultin colliding messages or signaling in the ranging sessions. Accordingly,where multiple ranging sessions in a distributed system may occursimultaneously, the lack of control or optimization of the rangingsessions may inhibit participation of responder UEs and may undermineranging and positioning of the UEs.

SUMMARY

A responder user equipment (UE) that is included in separate rangingsessions may determine whether there is a collision between that rangingsignals that it is assigned to broadcast in the separate rangingsessions. A collision in the ranging signals, for example, may bedetected when the ranging signals have the same frequencies andbroadcast times, e.g., the broadcast time of one ranging signal iswithin a predetermined amount of time for the other ranging signal. Whena collision in the ranging signals is detected, the responder UE sends amessage to the initiator UE indicating the possibility of a collision.The responder UE may additionally determine available times forbroadcasting the ranging signals and provide the available times to theinitiator UE or the initiator UE may determine available times. Theinitiator UE may reconstruct and initiate a new ranging session based onthe available times for broadcasting the ranging signal or may proceedwith the ranging session with the possibility that the responder UE willnot participate.

In one implementation, a method of ranging between user equipments (UEs)performed by a responder UE, includes receiving a first pre-rangingrequest message from a first initiator UE to initiate a first rangingsession, the first pre-ranging request message comprising first rangingsignal resources including a time and frequencies for the responder UEto broadcast a first ranging signal in the first ranging session;receiving a second pre-ranging request message from a second initiatorUE to initiate a second ranging session, the second pre-ranging requestmessage comprising second ranging signal resources including a time andfrequencies for the responder UE to broadcast a second ranging signal inthe second ranging session; determining a collision between the firstranging signal and the second ranging signal based on the first rangingsignal resources and the second ranging resources; sending a firstpre-ranging response message to the first initiator UE acknowledging thefirst pre-ranging request message; and sending a second pre-rangingresponse message to the second initiator UE indicating the collisionwith the second ranging signal resources for the second ranging signal.

In one implementation, a responder user equipment configured for rangingbetween UEs, includes a wireless transceiver configured to wirelesslycommunicate with entities in a wireless network; at least one memory;and at least one processor coupled to the wireless transceiver and theat least one memory, wherein the at least one processor is configuredto: receive a first pre-ranging request message from a first initiatorUE to initiate a first ranging session, the first pre-ranging requestmessage comprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; receive a second pre-ranging request messagefrom a second initiator UE to initiate a second ranging session, thesecond pre-ranging request message comprising second ranging signalresources including a time and frequencies for the responder UE tobroadcast a second ranging signal in the second ranging session;determine a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources; send a first pre-ranging response message tothe first initiator UE acknowledging the first pre-ranging requestmessage; and send a second pre-ranging response message to the secondinitiator UE indicating the collision with the second ranging signalresources for the second ranging signal.

In one implementation, a responder user equipment configured for rangingbetween UEs, the responder UE includes means for receiving a firstpre-ranging request message from a first initiator UE to initiate afirst ranging session, the first pre-ranging request message comprisingfirst ranging signal resources including a time and frequencies for theresponder UE to broadcast a first ranging signal in the first rangingsession; means for receiving a second pre-ranging request message from asecond initiator UE to initiate a second ranging session, the secondpre-ranging request message comprising second ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast asecond ranging signal in the second ranging session; means fordetermining a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources; means for sending a first pre-ranging responsemessage to the first initiator UE acknowledging the first pre-rangingrequest message; and means for sending a second pre-ranging responsemessage to the second initiator UE indicating the collision with thesecond ranging signal resources for the second ranging signal.

In one implementation, a non-transitory storage medium including programcode stored thereon, the program code is operable to configure at leastone processor in a responder user equipment for ranging between UEs, theresponder UE the program code comprising instructions to: receive afirst pre-ranging request message from a first initiator UE to initiatea first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; receive a second pre-ranging request messagefrom a second initiator UE to initiate a second ranging session, thesecond pre-ranging request message comprising second ranging signalresources including a time and frequencies for the responder UE tobroadcast a second ranging signal in the second ranging session;determine a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources; send a first pre-ranging response message tothe first initiator UE acknowledging the first pre-ranging requestmessage; and send a second pre-ranging response message to the secondinitiator UE indicating the collision with the second ranging signalresources for the second ranging signal.

In one implementation, a method of ranging between user equipments (UEs)performed by an initiator UE, includes transmitting a first pre-rangingrequest message to a responder UE to initiate a first ranging session,the first pre-ranging request message comprising first ranging signalresources including a time and frequencies for the responder UE tobroadcast a first ranging signal in the first ranging session; andreceiving a first pre-ranging response message from the responder UEindicating a collision between the first ranging signal resources forthe first ranging signal and second ranging signal resources for asecond ranging signal for a second initiator UE.

In one implementation, an initiator user equipment (UE) configured forranging between UEs, the initiator UE, includes a wireless transceiverconfigured to wirelessly communicate with entities in a wirelessnetwork; at least one memory; and at least one processor coupled to thewireless transceiver and the at least one memory, wherein the at leastone processor is configured to: transmit a first pre-ranging requestmessage to a responder UE to initiate a first ranging session, the firstpre-ranging request message comprising first ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast afirst ranging signal in the first ranging session; and receive a firstpre-ranging response message from the responder UE indicating acollision between the first ranging signal resources for the firstranging signal and second ranging signal resources for a second rangingsignal for a second initiator UE.

In one implementation, an initiator user equipment (UE) configured forranging between UEs, the initiator UE includes means for transmitting afirst pre-ranging request message to a responder UE to initiate a firstranging session, the first pre-ranging request message comprising firstranging signal resources including a time and frequencies for theresponder UE to broadcast a first ranging signal in the first rangingsession; and means for receiving a first pre-ranging response messagefrom the responder UE indicating a collision between the first rangingsignal resources for the first ranging signal and second ranging signalresources for a second ranging signal for a second initiator UE.

In one implementation, a non-transitory storage medium including programcode stored thereon, the program code is operable to configure at leastone processor in an initiator user equipment (UE) for ranging betweenUEs, the initiator UE, the program code comprising instructions to:transmit a first pre-ranging request message to a responder UE toinitiate a first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; and receive a first pre-ranging responsemessage from the responder UE indicating a collision between the firstranging signal resources for the first ranging signal and second rangingsignal resources for a second ranging signal for a second initiator UE.

BRIEF DESCRIPTION OF THE DRAWING

Non-limiting and non-exhaustive aspects are described with reference tothe following figures, wherein like reference numerals refer to likeparts throughout the various figures unless otherwise specified.

FIG. 1 illustrates a wireless communication system illustratingdistributed communications, including ranging signaling to supportmultiple ranging sessions and/or positioning.

FIG. 2 illustrates a signaling graph indicating the timing andfrequencies of various messages that may be sent and received by aninitiating UE and three responder UEs for a ranging or positioningsession.

FIG. 3 illustrates a graph showing two separate sets of ranging sessionsin which PRS signals to be broadcast by a responder collide.

FIG. 4 is a graph illustrating the determination of a collision in PRSbroadcast times and available broadcast times.

FIG. 5 illustrates a signaling flow for separate ranging sessions withcolliding PRS broadcast times, where a ranging session is rescheduled.

FIG. 6 illustrates a signaling flow for separate ranging sessions withcolliding PRS broadcast times, without rescheduling the rangingsessions.

FIG. 7 shows a schematic block diagram illustrating certain exemplaryfeatures of a UE.

FIG. 8 is a flow chart illustrating a method of ranging between UEsimplemented by a responder UE.

FIG. 9 is a flow chart illustrating a method of ranging between UEsimplemented by an initiator UE.

DETAILED DESCRIPTION

A distributed approach may be used for ranging and positioning ofvehicles, roadside units (RSU), and pedestrian and may avoid the needfor a centralized base station to coordinate and relay communications.Such communications may be used, for example, for automated driving andvehicle safety applications. Communications used in a distributedapproach may be made directly, e.g., between vehicles, or betweenvehicles and a RSU or pedestrian. These communications may includemessages and information elements (IEs) with which a vehicle may provideinformation necessary for automated driving.

For example, for safe operation of autonomous vehicles, the relativelocations or ranges to other vehicles needs to be determined. Variousapproaches may be used to derive the relative positions betweenvehicles. For example, relative positions of vehicles may be derivedusing ranging signaling. Ranging signals are sometimes referred to asphysical ranging signals, positioning ranging signals, positioningreference signals, or physical referencing signals, and may becollectively referred to herein as PRS signals. PRS signals, forexample, may be broadcast by a user equipment (UE) in a vehicle,sometimes referred to as V-UE, and received by other V-UEs and/orinfrastructure, e.g., RSU, or UEs held by a pedestrian, using directcommunication systems, such as dedicated short-range communication(DSRC), cellular Vehicle-to-Everything (C-V2X) communication, and even5G New Radio (NR) communications. PRS signals are used to determine arange to the broadcasting vehicle, e.g., using one way ranging,round-trip-time (RTT) positioning operations, or other standardpositioning operations such as time of arrival (TOA), time difference ofarrival (TDOA) or observed time difference of arrival (OTDOA).

In a distributed system, an individual UE is able to range with respectto other UEs that are nearby using messages and positioning signals thatare transmitted directly to the other UEs. In an RTT-based rangingsession, for example, multiple messages and signals are transmitted andreceived by each UE. For example, an initial set of pre-ranging signalmessages (pre-PRS messages) are transmitted and received to request andaccept a ranging session, followed by broadcasting the ranging signals(PRS signals) for measurement, which is followed by a set ofpost-ranging signal messages (post-PRS messages) that exchangemeasurement payloads. For RTT-based ranging and positioning, forexample, the time of arrival (TOA) and time of departure (TOD)measurements of transmitted and received PRS signals may be provided inthe post-PRS messages and used by each UE pair to determine the rangebetween the UEs. The pre-PRS and post-PRS messages may be sent over alicensed spectrum to guarantee reliability, while the PRS signals may bebroadcast over an unlicensed spectrum (e.g., to enjoy a larger availablebandwidth in e.g., UNI-III spectrum).

The distributed mechanism ensures a minimum overhead, but multiplenearby UEs may initiate separate ranging sessions independently of eachother. Thus, multiple uncoordinated ranging sessions may be autonomouslyinitiated by separate UEs. For example, without overhead communicationsto control ranging sessions, multiple UE may separately broadcast theirown pre-PRS signals to the same set of responder UEs resulting inindependent ranging sessions that include the same responder UEs andthat occur at the same time. For example, multiple V-UEs may initiateseparate ranging sessions with the same set of RSUs. Moreover, nearbypedestrian held UEs may likewise initiate ranging sessions with the sameset of RSUs. Thus, multiple separate ranging sessions may besimultaneously initiated with one or more of the same responder UEs. Theseparate ranging sessions, by way of example, may be initiated byinitiator UEs, e.g., because they are out of coverage from each otherand thus will not include the other initiator UE in the ranging sessionand/or do not receive the initiating pre-PRS message from the otherinitiator UE. Separate ranging sessions may be initiated by separateinitiator UEs for other reasons, such as limiting responder UEs to UEsthat know their positions (e.g., anchor UEs) and that can be used forpositioning of the initiator UE, etc.

A responder UE that is included in multiple simultaneous rangingsessions may have messages or signals that collide in the separateranging sessions. For example, a responder UE may receive a pre-PRSmessage from multiple initiator UEs that request PRS signals to bebroadcast by the responder UE on the same channel, e.g., CH 171, andapproximately the same time, and thus, collide. The responder UE may notbe able to use the same channel to broadcast PRS to both initiator UEsif the times for broadcasting the PRS signals in each ranging sessionare close.

Accordingly, in an implementation, as discussed herein, a responder UEthat receives multiple pre-ranging request messages that include timeand frequencies for broadcasting ranging signals may determine if acollision between the ranging sessions in the separate ranging sessionsexist. The collision may be detected if the time to broadcast theranging signals are within a predetermined amount of time of each otherand the same frequencies are to be used for broadcasting the rangingsignals. The responder UE may send an indication that there is acollision in the ranging signals to at least one of the initiator UEs.For example, the responder UE may send an acknowledgement of a firstinitiator UE and may send the indication of a collision to the otherinitiator UE(s). In some implementations, the responder UE may determinean available time for broadcasting additional ranging signal(s) and mayprovide the available time with the indication of collision. In someimplementations, an initiator UE that receives an indication ofcollision may continue with the ranging session and the responder UE maybroadcast the ranging signal if possible, i.e., the collision does notoccur. In another implementation, the initiator UE that receives theindication of collision may send another pre-ranging request with adifferent time for the responder UE to broadcast the ranging signals.Accordingly, the multiple ranging sessions may proceed with a reducedlikelihood of collision of signal transmission by overlapping responderUEs, thereby increasing the probability of successful ranging andpositioning of the UEs.

FIG. 1 illustrates a wireless communication system 100 illustratingdistributed communications, including ranging signaling to supportmultiple ranging sessions and/or positioning, as described herein.Wireless communication system 100 illustrates a first vehicle 102 with afirst wireless device, e.g., V-UE 102, in wireless communications withanother V-UE 104, illustrated as a second vehicle. The V-UE 102 and V-UE104 may comprise, but are not limited to, an on-board unit (OBU), avehicle or subsystem thereof, or various other communication devices.The V-UEs 102 and 104 function and provide communications on behalf oftheir associated vehicles and, accordingly, may be sometimes referred toherein simply as vehicles 102 and 104 or UEs 102 and 104. The first UE102 and second UE 104, for example, may be two vehicles traveling on aroad along with other vehicles, not illustrated.

The wireless communication system 100 may use, e.g.,Vehicle-to-Everything (V2X) communication standard, in which informationis passed between a vehicle and other entities within the wirelesscommunication network. The V2X services include, e.g., services forVehicle-to-Vehicle (V2V), Vehicle-to-Pedestrian (V2P),Vehicle-to-Infrastructure (V2I), and Vehicle-to-Network (V2N). The V2Xstandard aims to develop autonomous or semi-autonomous driving systems,such as Advanced Driver Assistance System (ADAS), which helps driverswith critical decisions, such as lane changes, speed changes, overtakingspeeds, and may be used to assist in parking as discussed herein. Lowlatency communications are used in V2X and are therefore suitable forprecise relative positioning, e.g., using ranging signals, such as oneway ranging, RTT, TDOA, etc.

In general, there are two modes of operation for V2X services, asdefined in Third Generation Partnership Project (3GPP) TS 23.285. Onemode of operation uses direct wireless communications between V2Xentities, which may sometimes be referred to as sidelink communication.The other mode of operation uses network based wireless communicationbetween entities. The two modes of operation may be combined, or othermodes of operation may be used if desired.

The wireless communication system 100 may operate using direct orindirect wireless communications between the UE 102 and UE 104. Forexample, the wireless communication may be over, e.g., Proximity-basedServices (ProSe) Direction Communication (PC5) reference point asdefined in 3GPP TS 23.303, and may use wireless communications underIEEE 1609, Wireless Access in Vehicular Environments (WAVE), IntelligentTransport Systems (ITS), and IEEE 802.11p, on the ITS band of 5.9 GHz,or other wireless connections directly between entities. Thus, asillustrated, UE 102 and UE 104 may directly communicate using with aVehicle-to-Vehicle (V2V) communication link 103. UE 102 and UE 104 maysimilarly directly communicate with roadside unit (RSU) 110 viaVehicle-to-Infrastructure (V2I) communication links 107 and 109,respectively. The RSU 110 may include a backhaul connection to anetwork, illustrated by wired connection 111, but may via a wireless Uuinterface to a base station. The RSU 110, for example, may be astationary infrastructure entity, that may support V2X applications andthat can exchange messages with other entities supporting V2Xapplications. An RSU may be a logical entity that may combine V2Xapplication logic with the functionality of base stations in a RAN, suchas an eNB, ng-eNB, or eLTE (referred to as eNB-type RSU) or a gNB, or UE(referred to as UE-type RSU). The RSU 110 may be used for ranging withUEs 102, 104, or other UEs, and because the position of the RSU 110 maybe known precisely, the RSU 110 may be used as an anchor UE with which aposition of the UE 102, 104 or other UEs may be determined. The RSU 110may sometimes be referred to herein as UE 110. The UEs 102, 104 and UE110 may communicate with additional entities, such as additionalvehicles, RSUs or with a UE 112 held by pedestrian 114 using directcommunication links. For example, UE 102 may communicate with UE 112 viaV2V communication link 113, UE 104 may communicate with UE 112 via V2Vcommunication link 115, and UE 110 may communicate with UE 112 via V2Icommunication link 117.

During direct communications with one or more entities in the V2Xwireless communication system 100, each entity may provide V2Xinformation, such as an identifier for the V2X entity, as well as otherinformation in messages such as Common Awareness Messages (CAM) andDecentralized Notification Messages (DENM) or Basic Safety Message(BSM), which may be used for, e.g., ADAS or safety use cases.

In other implementations, UE 102 and UE 104 may indirectly communicatewith each other, e.g., through the RSU 110 via the V2I communicationlinks 107 and 109, respectively or through other network infrastructure(not shown), e.g., using cellular vehicle-to-everything (CV2X). Forexample, vehicles may communicate via a base station in a Radio AccessNetwork (RAN), such as an evolved Node B (eNB) or next generationevolved Node B (ng-eNB) in LTE wireless access and/or evolved LTE (eLTE)wireless access or a NR Node B (gNB) in Fifth Generation (5G) wirelessaccess.

UEs 102 and 104 may initiate and perform ranging/positioning sessions,including sending pre-PRS messages, broadcasting PRS, and sendingpost-PRS messages on links 103, 107, 109, 113 or 115, with which therange or relative positions between UEs 102 and 104 may be determined.The PRS broadcast by UEs 102 and 104 may be any signal suitable forranging, e.g., as defined for DSRC or C-V2X. The PRS may be broadcast onlicensed or unlicensed spectrum. For example, in some implementations,PRS may be broadcast on one or more Unlicensed National InformationInfrastructure (UNII) radio bands including, for example, one or more ofthe UNII-1 radio band, the UNII-2A radio band, the UNII-2B radio band,or the UNII-3 radio band. When broadcasting on unlicensed spectrum,listen-before-transmit (LBT) protocols may be employed.

Where UEs 102 and 104 broadcast PRS in a V2V link 103, the range orrelative positions between UEs 102 and 104 may be determined directly.Where UE 102 and 104 broadcast PRS in V2I links 107 and 109 or via links113 and 115, the range or relative positions between UE 102 and UE 110or UE 112 and between UE 104 and UE 110 or UE 112 may be determineddirectly.

The direct wireless communications between the UE 102 and 104 and UE 110and UE 112, do not require any network infrastructure and enable lowlatency communications, which is advantageous for precise ranging orpositioning. Accordingly, such direct wireless communications may bedesirable for ranging over short distances, e.g., with nearby vehiclesor infrastructure.

The UEs, e.g., any of V-UE 102, V-UE 104, RSU 110, and UE 112, shown inFIG. 1 , may be configured to perform ranging and/or positioningoperations, such as RTT-based ranging.

FIG. 2 illustrates, by way of example, a signaling graph 200 indicatingthe timing and frequencies of various messages that may be sent andreceived by an initiator UE (UEX) and three responder UEs (UEA, UEB, andUEC) for a ranging or positioning session. For example, FIG. 2illustrates capabilities messages 201 and an RTT-based ranging session202, during which a number of messages are sent between an initiator UEand responder UEs, including pre-PRS messages 204 to request and accepta ranging session, the PRS signals 208 for measurement, and post-PRSmessages 208 to exchange measurement payloads. Each set of pre-PRS 204,PRS 206, and post-PRS 208 may be considered a single unit or PRS cycle.Each PRS cycle includes a pre-PRS message 204, PRS signal 206, andpost-PRS message 208, and may therefore be referred to herein as aranging session 202. The ranging sessions (PRS cycles) may be periodicwith a period T_r, and the capabilities messages may be periodic with aperiod T_c, where T_r_>T_c. In FIG. 2 , the signaling from the initiatorUEX is illustrated with white boxes that are labeled “X,” signaling froma first responder UEA is illustrated with gray boxes that are labeled an“A,” signaling from a second responder UEB is illustrated with hatchedboxes that are labeled with a “B,” and signaling from a third responderUEC are illustrated with block boxes that are labeled with a “C.” Thesignaling from the initiator UEX is the first box in each of the pre-PRSmessages 204, the PRS signals 206, and the post-PRS messages 208, and isfollowed by the responder UEs (UEA, UEB, and UEC).

As illustrated, the UEs, including the initiator UE and responder UEs,may broadcast capabilities messages 201. The capabilities messages arenot part of the ranging session but may include information that may beused by the initiator UE to initiate a ranging session with selectedUEs. For example, the capabilities message may be on the ITS spectrumand may include the UE ID, the ranging capability of the UE, the channelthat the UE is configured to use, MIMO (Multiple Input Multiple Output)capabilities, etc. The capabilities message may additionally indicatewhether the UE needs to determine its position or if its position isknown and it may serve as an anchor UE for positioning other UEs. Itshould be understood that while FIG. 2 illustrates the capabilitiesmessages 201 as having the same order as the messages in the rangingsession 202, the order may, in fact, differ.

The pre-PRS messages 204 (e.g., pre-ranging messages) are used by theUEs to request and acknowledge a ranging session. As illustrated, thepre-PRS messages 204 may be transmitted on a licensed spectrum toguarantee reliability. The pre-PRS messages 204 may be broadcast orunicast, e.g., with Radio Resource Control (RRC) connections. Theinitiator UEX broadcasts an initial pre-PRS message 204 (PrePRSRequest)to initiate the ranging session between the initiator UE and theresponder UEs and to provide information for the ranging session(illustrated with the white box labeled X). For example, the pre-PRSmessage 204 from the initiator UE, may include IDs for participatingUEs, i.e., the initiator and responder IDs. The pre-PRS request messagemay include a ranging session ID, the channel for the PRS broadcast bythe initiator UEX and responder UEs, the PRS broadcast time, the maximumlisten before transmit (LBT) time, etc. The pre-PRS request message fromthe initiator UEX for example may include a PRS ID that will be used bythe initiator UE, and in some implementations, the PRS ID to be used bythe responder UEs. If the PRS ID will be fixed over multiple PRSexchanges (e.g., for multiple units in the ranging session 202), theinitiator UE may include an ID associated with the current PRS exchange,e.g., a session ID. The initiator UE may determine when the PRS signals206 will be transmitted, which, for example, may be configured from anupper layer in the initiator UE. The initiator UE may indicate thetiming of the PRS by sending the time slot number nears to the desiredPRS transmission time. In some implementations, the time slot may besubject to local clock error. The initiator UE may further provide thetiming of PRS to be sent by the responder UEs, as well as a maximum LBTtime or other maximum predetermined delay for broadcasting the PRS. Theinitiator UE may further indicate the frequency that will be used tobroadcast the PRS signal 206 by the initiator UE and the responder UEs.For example, the frequency of PRS may be selected from an available setof total bandwidths or the frequency of PRS may be selected by sensingthe interference and choosing one or more channels whose averageinterference Reference Signal Receive Power (RSRP) is less than athreshold. The initiator UE may indicate the number of PRS cycles thatit will execute during the ranging session 202. The number of PRS cyclesmay be configured from an upper layer. The pre-PRS message for each PRScycle, for example, may indicate the current PRS cycle with respect tothe total PRS cycles requested, where the number of the current cycleincrements after completion of each cycle.

The initial pre-PRS request message from the initiator UE is receivedand decoded by the responder UEs, which are identified in the initialpre-PRS message. The responder UEs may send pre-PRS messages 204 inresponse (illustrated with gray, hatched, and black boxes labeled withA, B, C, respectively) which may acknowledge the pre-PRS requestmessage, which may additionally provide information for the rangingsession. Each responder UE may indicate the PRS ID that it will use ormay indicate that it will use the PRS ID that was indicated in theinitial pre-PRS message. If the PRS ID will be fixed over multiple PRSexchanges (e.g., multiple PRS cycles in the ranging session 202), theresponder UE may include the ID associated with the current PRSexchange, e.g., a session ID, that was received in the initial pre-PRSmessage from the initiator UE. The responder UEs may broadcast thepre-PRS messages 204, which may be received by the initiator UE (andother responder UEs). In some implementations, each responder UE maytransmit the pre-PRS message 204 using unicast with RRC connection tothe initiator UE.

The PRS signals 206 are exchanged by the participating UEs. Theinitiator UE and responder UEs know the expected timing and frequenciesof the PRS signals and know the PRS ID (and any session ID used with theexchanged) that is used to broadcast the PRS signals 206. The PRSsignals 206 may be, for example, a Quadrature Phase Shift Keying (QPSK)modulated pseudo-noise (PN) sequence and may include the ranging sessionID. The PRS signals 206 may be broadcast on an unlicensed spectrum,which may be subject to LBT constraints. In some implementations, whenusing the unlicensed spectrum, the initiator UEX may reserve thetransmission for responder UEs UEA, UEB, and UEC, so that the responderUEs may not need to perform LBT. For example, the initiator UEXbroadcasts its PRS signal 206 (white box labeled with X) at thedetermined time that was indicated in the initial pre-PRS message 204.In some implementations, the initiator UE broadcasts its PRS signal atthe determined time plus a random waiting time due to the LBTconstraints when the PRS signal is deployed in the unlicensed spectrum.In some implementations, the LBT may be a Category 2 LBT with a fixedwindow Clear Channel Assessment (CCA) or a Category 4 LBT with a varyingwindow CCA. The initiator UE uses the PRS signal that corresponds to thePRS ID and uses the frequency resources that were indicated in itsinitial pre-PRS message 204. The initiator UE stores the time instancethat the PRS signal is broadcast, and the responder UEs store the timeinstance that the PRS signal is received. In some implementations, thetime instances may be subject to local clock error.

Similar to the initiator UE, each responder UE broadcasts its PRS signal206 (illustrated with gray, hatched, and black boxes labeled with A, B,C, respectively) at the time and frequencies that were assigned in theinitial pre-PRS message 204 by the initiator UE. In someimplementations, each responder UE may broadcast its PRS signal at thedetermined time plus a random waiting time due to the LBT constraintswhen the PRS signal is deployed in the unlicensed spectrum. In someimplementations, the LBT may be a Category 2 LBT with a fixed window CCAor a Category 4 LBT with a varying window CCA. Each responder UE usesthe PRS signal that corresponds to the PRS ID that was indicated in itspre-PRS messages 204. Each responder UE stores the time instance thatits PRS signal is broadcast, and the initiator UE (and optionally otherresponder UEs) store the time instance that the PRS signal from eachresponder UE is received. In some implementations, the time instancesmay be subject to local clock error.

Thus, each UE records the time of departure (ToD) of its broadcast PRSsignal and measures the time of arrival (ToA) of the PRS signal receivedfrom the other UEs. The PRS signal may be any signal suitable forranging, e.g., as defined for DSRC or C-V2X, such as QPSK modulated PNsequence. The ToA and ToD resolution of the PRS signals increase with anincreased frequency bandwidth. In some implementations, the angle ofdeparture (AoD) and angle of arrival (AoA) of the broadcast and receivedPRS signals may also be measured. Broadcasting on an unlicensed spectrumis advantageous as a wider frequency band is available. For example, insome implementations, PRS may be broadcast on one or more UNII radiobands including, for example, one or more of the UNII-1 radio band, theUNII-2A radio band, the UNII-2B radio band, or the UNII-3 radio band.

The post-PRS messages 208 are sent by each UE to exchange measurementpayloads. As illustrated, the post-PRS messages 208 may be transmittedon a licensed spectrum to guarantee reliability. In someimplementations, the post-PRS messages 208 may be broadcast or unicastwith RRC connection. The initiator UEX sends its post-PRS message 208(illustrated as the white box labeled with X) and indicates when itbroadcast the PRS signal 206 (ToD) and when the PRS signals from theresponder UEs were received (ToA). In some implementations, the ToA maybe computed as a relative time with respect to the ToD of its broadcastPRS signal, and the relative time may be provided. In someimplementations, the relative time may be approximated to the closestmultiple of time scale shared by the initiator UE and the responder UEs.In some implementations, the initiator UE may provide an indication ofits location in the post-PRS message 208, if known. For example, thelocation of the initiator UE may be the location at a specific time,such as the broadcast time of its PRS signal or the arrival time of thePRS signal from a responder UE. The post-PRS message 208 may furtherinclude the AoD of its PRS signal 206 and the AoA of the PRS signals 206received from the responder UEs, the orientation of initiator UE, abroadcast indicator of the PRS signal 206, a reception indicator of PRSfrom the responder UEs, as well as other related measurements, e.g.,including map information, the locations of reflectors with respect tothe UE, etc.

Similar to the initiator UE, each responder UEs sends its post-PRSsignal 208 (illustrated with gray, hatched, and black boxes labeled withA, B, C, respectively) to provide the measurement payloads. Eachresponder UE may indicate whether it received the PRS signal from theinitiator UE and may indicate when it broadcast the PRS signal 206 (ToD)and when the PRS signals from the initial UE (and optionally from otherresponder UEs) was received (ToA). In some implementations, the ToD maybe computed as a relative time with respect to the ToA of the PRS signalfrom the initiator UE (and optionally with respect to the ToA of the PRSfrom other responder UEs). In some implementations, the relative timemay be approximated to the closest multiple of time scale shared by theinitiator UE and the responder UE. In some implementations, theresponder UE may provide an indication of its location in the post-PRSmessage 208, if known. For example, the location of the responder UEprovided may be the location at a specific time, such as the arrivaltime of PRS signal from the initiator UE or the departure time of itsbroadcast PRS signal. The post-PRS message 208 may further include theAoD of its PRS signal 206 and the AoA of the PRS signals 206 receivedfrom the initiator UEX (and optionally received from the other responderUEs), the orientation of initiator UE, a broadcast indicator of the PRSsignal 206, a reception indicator of PRS from the responder UEs, as wellas other related measurements, e.g., including map information, thelocations of reflectors with respect to the UE, etc.

After receiving the post-PRS messages, the initiator UE may compute itsrange (and in some implementations its location), e.g., using a Kalmanfilter, and then may transmit the next cycle of pre-PRS messages at atime that is indicated by an upper layer or that is autonomouslydetermined by the initiator UE.

The time between the first pre-PRS message 204 and the last post-PRSmessage 208 may be the duration of the ranging session and may be, e.g.,100 msec. The duration of each broadcast PRS signals 206 may be, e.g.,47 μsec. In some implementations, multiple PRS cycles, e.g., multipleinstances of pre-PRS messages 204, PRS 206, and post-PRS messages 208,may be used together to provide higher accuracy.

Both the initiator UE and the responder UEs may determine the rangebetween itself and each other UE in the ranging session based on the ToDand the ToA of the broadcast PRS signals. For example, the RTT betweenany pair of UEs (which may be any pair of initiator and responder UEs)may be determined based on the ToD_(i) and ToA_(i) for the PRS_(i)signals (where i=1 for PRS broadcast from a first UE and i=2 for PRSbroadcast by a second UE), as the difference between the ToD₁ and ToA₂minus the difference between the ToA₁ and the ToD₂, e.g., as follows.RTT=(ToD₁−ToA₂)−(ToA₁−ToD₂)  eq. 1

The RTT value is the round-trip time for the signal, and thus, the range(distance) between the UE₁ and UE₂ may be determined as RTT/2c, where cis the speed of light.

If the position of one or more responder UEs is known, the range betweenthe initiator UE and the responder UEs may be used along with the knownposition of the one of the responder UE to determine the position of theother UE, and thus, the ranging session may be a positioning session.The responder UEs with known positions that may be used for positioningmay sometimes be referred to herein as anchor UEs. The positions ofanchor UEs may be provided to other UEs through messaging, e.g., in thepre-PRS messages or in the post-PRS messages. If the range to multipleanchor UEs is determined, the positions of the multiple anchor UEs maybe used in multilateration to determine the position of the initiator UE(or other responder UEs).

The angle measurements, e.g., AoD, and AoA, may be used, e.g., forassistance in positioning. By way of example, based on the range betweentwo UEs and a measured AoA, the relative positions of the two UEs may bedetermined. With the relative positions of the UEs determined, if theactual position of one of the UEs is known (which may be provided, e.g.,in the pre-PRS messages 204 or post-PRS messages 208), the actualposition of the other UE may be determined. If the position of two UEsare known by a third UE, the ranges between the third UE and each of theother two UEs will produce two possible positions for the third UE,which may be resolved based on AoD/AoA information. The AoD may beuseful if the resolution of the AoA is poor or incorrect, for example.AoD may be measured, e.g., based on a known orientation of the UE (forexample, determined by a magnetometer), and the direction of thetransmitted signal relative to the UE (e.g., relative to an antennaarray of the UE used for beamforming). The AoA may be measured based onthe phase difference of a received signal at different antenna elementsof an antenna array and the known orientation of the UE, for exampledetermined by a magnetometer). Additionally, geographic constraints maybe used to assist in positioning, for example, by constraining possiblepositions of a vehicle based on positions that are accessible to avehicle, such as a road.

As discussed above, due to the distributed mechanism for ranging, it ispossible that multiple UEs may initiate independent ranging sessionsthat include at least some of the same responder UEs at approximatelythe same time. For example, two initiating UEs may separately broadcasttheir own pre-PRS signals to the same set of responder UEs resulting intwo independent ranging sessions that include the same responder UEs andthat occur at the same time. By way of illustration, an initiator UEXmay send a pre-ranging request message to responder UEA with rangingsession ID 182, and PRS channel 171, and a second initiator UEY may senda separate pre-ranging request message to the same responder UEA with aranging session ID 183, and PRS channel 171. The responder UEA, thus, isincluded in both ranging sessions ID 182 and ID 183, but it might not beable to use channel 171 for broadcasting the PRS in both rangingsessions for initiator UEX and initiator UEY if the PRS broadcast timesare close.

FIG. 3 , by way of example, illustrates a graph showing two separatesets of ranging sessions 302 and 312 in which PRS signals 306 and 316for a responder UEA that may collide. A first ranging session 302, whichincludes pre-PRS messages 304, PRS signaling 306, and post-PRS messages308 is between a first initiator UEX and responder UEA. The signalingfrom the initiator UEX is illustrated with white boxes that are labeled“X” and the signaling from the responder UEA is illustrated with grayboxes that are labeled with an “A.” It should be understood that theranging sessions 302 and 312 may include multiple responder UEs, butthat only responder UEA is illustrated. A second ranging session 312,which includes second pre-PRS messages 314, second PRS signaling 316,and second post-PRS messages 318 is between a second initiator UEY andthe same responder UEA. The signaling from the initiator UEY in rangingsession 312 is illustrated with dark gray boxes that are labeled “Y” andthe signaling from the responder UEA is illustrated with light grayboxes that are labeled with an “A.”

The first initiator UEX may send the pre-PRS message 304 to theresponder UEA that, as discussed above, may include among other thingsthe ranging session ID, the channel for the PRS broadcast by theresponder UEA, the time for the PRS broadcast by the responder UEA, andthe maximum LBT or other delay time permitted for the broadcast PRS. Thesecond initiator UEY may send the second pre-PRS message 314 to theresponder UEA shortly after pre-PRS message 304 sent by the firstinitiator UEX. The second pre-PRS message 314, similar to the firstpre-PRS message 304, may include among other things the ranging sessionID, the channel for the PRS broadcast by the responder UEA, the time forthe PRS broadcast by the responder UEA, and the maximum LBT or otherdelay time permitted for the broadcast PRS. The second pre-PRS message314 may include the same channel and time for the PRS broadcast by theresponder UEA as provided in the first pre-PRS message 304, as indicatedby line 320 between the PRS signal 306 from the responder UEA (with thelight gray box labeled A) in first ranging session 302 and the PRSsignal 316 from the responder UEA (with the light gray box labeled A) insecond ranging session 312.

Thus, as can be seen in FIG. 3 , the responder UEA's broadcast time forthe first PRS signals 306 in the first ranging session 302 and thebroadcast time for the second PRS signals 316 in the second rangingsession 312 may be the same or nearly the same, as illustrated by line320. The responder UEA cannot broadcast distinct PRSs to both rangingsessions 302 and 312 simultaneously, e.g. because the ranging session IDfor the two ranging sessions is different and result in different PRSsequence ID. Accordingly, with the first PRS 306 and second PRS 316assigned the same frequency channel and the same broadcast times, theresponder UEA will not be able to broadcast the PRS signal at theassigned time for both ranging sessions.

Accordingly, in one implementation, if the responder UEA determines thatthe PRS assigned in multiple ranging sessions collide, the responder UEAmay send a message (e.g., the pre-PRS response message 314 illustratedwith the gray box labeled A) to the second initiator UEY indicating thatthere is a collision. In some implementations, the responder UEA mayfurther provide an indication of an available time for PRS broadcast.The first initiator UEX will proceed with the first ranging session 302and the second initiator UEY may proceed with the second ranging session312, possibly without responder UEA, or may reconstruct the secondranging session with a new broadcast time for the second PRS for theresponder UEA and send a new pre-PRS request message to the responderUEA with the new PRS broadcast time for the responder UEA.

FIG. 4 is a graph 400 illustrating the determination by responder UEA ofa collision in PRS broadcast times and available broadcast times. FIG. 4illustrated along a timeline a first PRS broadcast time (Btime) (asindicated by arrow 402) and associated reserved LBT time 404 (or otherpredetermined delay time) along with a second PRS broadcast time (Btime)(as indicated by arrow 406). In some instances, for example, the firstPRS broadcast time 402 and reserved LBT time 404 may be assigned by thefirst initiator UEX for the first PRS 306, e.g., assigned in the pre-PRSrequest message 304 illustrated with the white box labeled X in FIG. 3 ,and the second PRS broadcast time 406 may be assigned by the secondinitiator UEY for the second PRS 316, e.g., assigned in the pre-PRSrequest message 314 illustrated with the dark gray box labeled Y inshown in FIG. 3 . However, in some instances, the second initiator UEYmay assign the second PRS 316 with a broadcast time that is before thebroadcast time assigned to the first PRS 306, in which case the firstPRS broadcast time 402 and reserved LBT time 404 illustrated in FIG. 4may correspond to the second PRS 316 shown in FIG. 3 and the second PRSbroadcast time 406 may correspond to the first PRS 306 shown in FIG. 3 .Nevertheless, for ease of reference, as discussed herein (unlessotherwise indicated) the first PRS broadcast time 402 and reserved LBTtime 404 in FIG. 4 corresponds to the first PRS 306 in FIG. 3 and thesecond PRS broadcast time 406 in FIG. 4 corresponds to the second PRS316 in FIG. 3 .

If the assigned frequencies for the PRS broadcasts for the multipleranging sessions are the same, the responder UEA may determine that thePRS for the ranging sessions collide if the second PRS broadcast time406 is within a predetermined amount of time from the first PRSbroadcast time 402. FIG. 4 , for example, illustrates the predeterminedamount of time for determining a collision (sometimes referred to hereinas collision threshold) with block 408. The collision threshold 408, forexample, may be the full duration of the reserved LBT time 404 (or otherpredetermined delay time). Because the reserved LBT time is the maximumLBT time, it is likely that the first PRS will be broadcast before theend of the reserved LBT time 404, and accordingly, the predeterminedcollision threshold 408 may be less than the reserved LBT time 404 ifdesired.

As illustrated in FIG. 4 , the second PRS broadcast time 40×6 fallswithin the collision threshold 408 from the first PRS broadcast time402, and thus, the first PRS and second PRS are determined to collide.Thus, the responder UEA sends a message to the second initiator UEYindicating that the assigned PRS collides with another PRS. For example,referring to FIG. 3 , the responder UEA may send the responding pre-PRSmessage 314 (illustrated with light gray box labeled A) to the secondinitiator UEY with a no acknowledgement (NACK) message to indicate thatthe assigned PRS collides with the PRS in another ranging session, butmay send the responding pre-PRS message 304 to the first initiator UEXacknowledging the ranging session.

Additionally, the responder UEA may further determine a time that isavailable for broadcasting the second PRS and may provide an indicationof the available time for the second PRS to the second initiator UEY.For example, as illustrated in FIG. 4 , the responder UEA has timeavailable for the second PRS before the first broadcast time 402(illustrated with block 410) and after the reserved LBT time 404(illustrated with block 412). In some implementations, the time betweenthe collision threshold 408 and the end of the reserved LBT time 404 (ifany) (e.g., indicated with block 414) may be treated by the responderUEA as available time for the second PRS, although there is a chancethat LBT for the first PRS will extend past the collision threshold 408.The responder UEA may provide the available time for broadcasting thesecond PRS to the second initiator UEY. For example, the responder UEAmay define the available time based on an initial time of blocks 410 and412 and their durations, by the start times and end times of the blocks410 and 412, or may provide the first broadcast time 402 and optionallythe reserved LBT time 404 (or the predetermined collision threshold408), from which the initiator UEY can determine available times forbroadcast of the PRS.

In some implementations, the responder UEA may not provide the availabletime initiator UEY and the initiator UEY may determine available timesfor PRS to be broadcast by the responder UEA based on the second PRSbroadcast time 406.

Various actions are possible by the initiator UEY after receiving anindication of a PRS collision by responder UEA. For example, in oneimplementation, the initiator UEY may simply continue with the secondranging session with responder UEA and other responder UEs. If theresponder UEA is able, it will broadcast the second PRS at the assignedsecond PRS broadcast time 406 (e.g., there is in fact no collision withthe first PRS broadcast time 402 because the first PRS is broadcastbefore the second PRS broadcast time 406). Additionally, if the firstPRS cannot be broadcast until after the second PRS broadcast time 406but is broadcast before the reserved LBT time for the second PRSbroadcast time, then the responder UEA may still broadcast the secondPRS. It may be advantageous for the initiator UEY to proceed with thesecond ranging session, even if the responder UEA may not broadcast itsPRS, for example, if there are many responder UEs and the initiator UEYdoes not need to presence of the PRS signal from responder UEA.

In another implementation, if the initiator UEY receives the availabletimes for broadcast from the responder UEA, the initiator UEY mayreconstruct the second ranging session to avoid the PRS collision, e.g.,using a different second PRS broadcast time for the responder UEA thatfalls within the available broadcast times. The initiator UEY, forexample, may send a new pre-PRS request message for the new secondranging session to all responder UEs. The new pre-PRS request messagemay include the same parameters as used in the original pre-PRS requestmessage for the second ranging session but may include a new rangingsession ID and the different second PRS broadcast time for the responderUEA (e.g., the PRS broadcast times for other responder UEs may not bechanged).

In another implementation, the responder UEA may not send availabletimes for broadcast and the initiator UEY may determine available timesfor PRS broadcast by the responder UEA without assistance from theresponder UEA. For example, once the initiator UEY receives anindication of a PRS collision from the responder UA, the initiator UEYmay estimate an available time for PRS broadcast by the responder UEAbased on the initial second PRS broadcast time 406 and a buffer time 414around the second PRS broadcast time 406. The buffer time 414, forexample, may be a predetermined amount of time before and after thesecond PRS broadcast time 406 that the initiator UEY will assume thatthe responder UEA is not able to broadcast the second PRS, and thus, theinitiator UEY may assume times outside of the buffer time 414 areavailable broadcast times for the responder UEA. The duration of thebuffer time 414, for example, may be based on the reserved LBT timeand/or a collision threshold after the second PRS broadcast time 406 andbefore the second PRS broadcast time 406. For example, the secondinitiator UEY may not know if the assigned second PRS 316 (shown in FIG.3 ) is after or before the other colliding PRS, and accordingly, buffertime both before and after the second PRS broadcast time 406 is used.

Once the initiator UEY determines the available broadcast times for theresponder UEA, the initiator UEY may reconstruct the second rangingsession to avoid the PRS collision, e.g., using a different second PRSbroadcast time for the responder UEA that falls within the availablebroadcast times. The initiator UEY, for example, may send a new pre-PRSrequest message for the new second ranging session to all responder UEs.The new pre-PRS request message may include the same parameters as usedin the original pre-PRS request message for the second ranging sessionbut may include a new ranging session ID and the different second PRSbroadcast time for the responder UEA (e.g., the PRS broadcast times forother responder UEs may not be changed).

FIG. 5 illustrates an example of a signaling flow 500 for separateranging sessions initiated by a first initiator UEX 502 and a secondinitiator UEY 504 and that include responder UEA and colliding PRSbroadcast times, where the second initiator UEY 504 rescheduling thesecond ranging session, as discussed herein. The initiator UEX 502,initiator UEY 504, and responder UEA 506 may be one or more of thevehicle based UEs (V-UE) 102 and 104, RSU 110 or UE 112, as described inFIG. 1 . It should be understood that FIG. 5 illustrates the signalingfor multiple ranging procedures involving only one responder UE, e.g.,UEA 506, but that additional responder UEs may be present, which wouldinvolve additional communications similar to that shown in FIG. 5 . Asillustrated, the communications between the UEs 502, 504, and 506 inFIG. 5 may be direct communications between the entities and may notinvolve infrastructure devices, such as base stations, to forward themessages between the entities.

At stage 1A, the first initiator UEX 502 sends a pre-PRS message(pre-ranging message) to request a ranging session with responder UEA506. The pre-PRS message may be transmitted via a licensed spectrum. Thepre-PRS message may indicate ranging signal properties to be used by theresponder UEA 506 (as well as the initiator UEX and any other responderUEs) in the ranging session with initiator UEX 502, such as a session IDand PRS resources, including frequency channel and timing instancesincluding the PRS broadcast time and reserved LBT time (or other delaytime), and PRS identifier (ID).

At stage 1B, the second initiator UEY 504 sends a pre-PRS message torequest a ranging session with the responder UEA 506. The pre-PRSmessage of stage 1B is after the pre-PRS message of stage 1A, and thus,the ranging session initiated by the pre-PRS message in stage 1A issometimes referred to as the first ranging sessions and the rangingsession initiated by the pre-PRS message in stage 1B is sometimesreferred to as the second ranging sessions. Similar to stage 1A, thepre-PRS message sent in stage 1B may be transmitted via a licensedspectrum and may indicate ranging signal properties to be used in theranging session by the responder UEA 506 (as well as the initiator UEY504 and any other responder UEs) in the second ranging session withinitiator UEY 504, such as a session ID and PRS resources, includingfrequency channel and timing instances including the PRS broadcast timeand reserved LBT time (or other delay time), and PRS identifier (ID).

At stage 2, the responder UEA 506 determines if a collision existsbetween the first PRS and second PRS assigned respectively in the firstpre-PRS message of stage 1A and the second pre-PRS message of stage 1B.As discussed, e.g., in FIG. 4 , a collision may be determined if the PRSsignals for both ranging sessions are assigned the same frequencychannels and if a second PRS broadcast time is within a predeterminedamount of time (e.g., collision threshold) of the first PRS broadcasttime. The duration of the collision threshold may be predetermined and,in some implementations, may be based on the approximate duration of areserved LBT time (or other delay time), e.g., the collision thresholdmay be a percentage (e.g., 100%, 80%, 60%, etc.) of the reserved LBTtime associated with the first PRS broadcast. Other considerations andfactors may be used to determine the duration of the collisionthreshold. In some implementations, the responder UEA 506 may furtherdetermine the available times for PRS broadcast, as illustrated in FIG.4 . For example, the available times may be determined based on timesbefore the first PRS broadcast time and after the reserved LBT time orafter the collision threshold time.

At stage 3, the responder UEA 506 sends a pre-PRS message (pre-rangingmessage) to the first initiator UEX 502 in response to the pre-PRSrequest of stage 1A, acknowledging the request, thereby indicating thatthe responder UEA 506 accepts the request for the ranging session frominitiator UEX 502. The pre-PRS message of stage 4A may be transmitted ona licensed spectrum.

At stage 4, the responder UEA 506 sends a pre-PRS message (pre-rangingmessage) to the second initiator UEY 504 in response to the pre-PRSrequest of stage 1B. Due to the collision of the second PRS assigned inthe second pre-PRS message of stage 1B with the first PRS assigned inthe first pre-PRS message of stage 1A, the responding pre-PRS message instage 4 includes an indication of a PRS collision, e.g., using a noacknowledgement (NACK) message. In some implementations, the responderUEA 506 may include an indication of available PRS broadcast times inthe pre-PRS message in stage 4. The indication of available PRSbroadcast times, for example, may be the start and end times of theavailable times, the start times and durations of the available times,the first PRS broadcast time and optionally either the reserved LBT timeor collision threshold duration, etc. The pre-PRS message of stage 4 maybe transmitted on a licensed spectrum.

At stage 5, the initiator UEY 504 may determine the available PRSbroadcast times for the responder UEA 506, e.g., from the available PRSbroadcast time provided in the pre-PRS message of stage 4, or if theresponder UEA 506 does not include the available PRS broadcast timeprovided in the pre-PRS message of stage 4 the initiator UEY 504 maydetermine the available time independently. For example, as discussed inFIG. 4 , the initiator UEY 504 may use a buffer time before and afterthe assigned second PRS broadcast time to define times during whichthere may be a PRS collision for the responder UEA 506, and timesoutside of the buffer times may be determined to be available PRSbroadcast times for the responder UEA 506. The initiator UEY 504 mayreconstruct the second ranging session based on the available PRSbroadcast time for the responder UEA 506.

At stage 6, the second initiator UEY 504 sends another pre-PRS messageto request the second ranging session with the responder UEA 506. Thepre-PRS message of stage 6 may be similar to the pre-PRS message ofstage 1B (including ranging signal properties to be used in the rangingsession by the initiator UEY 504 and any other responder UEs), but mayinclude a new session ID and the reconstructed PRS resources for theresponder UEA 506, including the frequency channel and new timinginstances including the new PRS broadcast time and reserved LBT time (orother delay time), and PRS identifier (ID).

At stage 7, the responder UEA 506 sends a pre-PRS message (pre-rangingmessage) to the second initiator UEX 502 in response to the pre-PRSrequest of stage 6, acknowledging the request, thereby indicating thatthe responder UEA 506 accepts the request for the ranging session fromthe second initiator UEY 504. The pre-PRS message of stage 4A may betransmitted on a licensed spectrum.

At stage 8A, the first initiator UEX 502 broadcasts a PRS signal using aset of PRS resources that were identified in the pre-PRS message ofstage 1A. The PRS signal may be broadcast on an unlicensed spectrum inorder to use a wide frequency band. The first initiator UEX 502 recordsthe ToD of the PRS signal and in some implementations the AoD of the PRSsignal and the responder UEA 506 records the ToA of the PRS signal andin some implementations measures and records the AoA of the PRS signal.

At stage 8B, in response to receiving the PRS signal in stage 8A, theresponder UEA 506 broadcasts a PRS signal using the PRS resources(including frequency channel, PRS broadcast time and reserved LBT time)assigned in the pre-PRS message of stage 1A. The PRS signal may bebroadcast on an unlicensed spectrum in order to use a wide frequencyband. The responder UEA 506 records the ToD of the PRS signal and insome implementations the AoD of the PRS signal and the first initiatorUEX 502 records the ToA of the PRS signal and in some implementationsmeasures and records the AoA of the PRS signal.

At stage 9A, the second initiator UEY 504 broadcasts a PRS signal usinga set of PRS resources that were identified in the pre-PRS message ofstage 6. The PRS signal may be broadcast on an unlicensed spectrum inorder to use a wide frequency band. The second initiator UEY 504 recordsthe ToD of the PRS signal and in some implementations the AoD of the PRSsignal and the responder UEA 506 records the ToA of the PRS signal andin some implementations measures and records the AoA of the PRS signal.

At stage 9B, in response to receiving the PRS signal in stage 9A, theresponder UEA 606 broadcasts a PRS signal using the PRS resources(including frequency channel, the revised PRS broadcast time andreserved LBT time) assigned in the pre-PRS message of stage 6. Becausethe PRS signal in stage 9B is broadcast using the revised PRS broadcasttime, there is no collision with the PRS broadcast in stage 8B. The PRSsignal in stage 9B may be broadcast on an unlicensed spectrum in orderto use a wide frequency band. The responder UEA 506 records the ToD ofthe PRS signal and in some implementations the AoD of the PRS signal andthe second initiator UEY 504 records the ToA of the PRS signal and insome implementations measures and records the AoA of the PRS signal.

At stage 10A, the first initiator UEX 502 sends a post-PRS message tothe responder UEA 506 indicating the ToD, and in some implementationsthe AoD, of the PRS signal broadcast at stage 8A and indicating the ToA,and in some implementations the AoA, of the PRS signal received at stage8B. If the position of the first initiator UEX 502 is known, thepost-PRS message may further include a current position of the firstinitiator UEX 502.

At stage 10B, the responder UEA 506 sends a post-PRS message to thefirst initiator UEX 502 indicating the ToA, and in some implementationsthe AoA, of the PRS signal received at stage 8A and indicating the ToD,and in some implementations the AoD, of the PRS signal broadcast atstage 8B. If the position of the responder UEA 506 is known, thepost-PRS message may further include a current position of the responderUEA 506.

At stage 11A, the second initiator UEY 504 sends a post-PRS message tothe responder UEA 506 indicating the ToD, and in some implementationsthe AoD, of the PRS signal broadcast at stage 9A and indicating the ToA,and in some implementations the AoA, of the PRS signal received at stage9B. If the position of the second initiator UEY 504 is known, thepost-PRS message may further include a current position of the secondinitiator UEY 504.

At stage 11B, the responder UEA 506 sends a post-PRS message to thesecond initiator UEY 504 indicating the ToA, and in some implementationsthe AoA, of the PRS signal received at stage 9A and indicating the ToD,and in some implementations the AoD, of the PRS signal broadcast atstage 9B. If the position of the responder UEA 506 is known, thepost-PRS message may further include a current position of the responderUEA 506.

At stage 12A, the first initiator UEX 502 may determine the rangebetween UEX 502 and responder UEA 506 based on the ToD and ToA of thePRS signals broadcast in stages 8A and 8B. For example, the range may bedetermined based on the ToD_(i) and ToA_(i) for the PRS_(i) signals(where i=1 for PRS broadcast by the initiator UEX 502 and i=2 for PRSbroadcast by the responder UEA 506) as:

$\begin{matrix}{{Range} = {\frac{\left( {{ToD}_{1} - {ToA}_{2}} \right) - \left( {{ToA}_{1} - {ToD}_{2}} \right)}{2c}.}} & {{eq}.2}\end{matrix}$

If the position of the responder UEA 506 is known, e.g., provided inpost-PRS message in stage 10B, along with additional information, suchas AoA or AoD of the PRS signals or positions and ranges for otherresponder UEs (not shown in FIG. 5 ), or geographic information, such asstreet locations, the position of the initiator UEX 502 may bedetermined using, e.g., multilateration and constraints pursuant to theAoA or AoD of the PRS signals and geographic information.

At stage 12B, the second initiator UEY 504 may determine the rangebetween UEY 504 and responder UEA 506 based on the ToD and ToA of thePRS signals broadcast in stages 9A and 9B, in a manner similar to thatdescribed in stage 12A. The position of the initiator UEY 504 may alsobe determined in a manner similar to that described in stage 12A.

At stage 12C, the responder UEA 506 may determine the range between UEA506 and the first initiator UEX 502 and the range between UEA 506 andsecond initiator UEY 504, based on the ToA and ToD of the PRS signalsbroadcast in stages 8A and 8B and broadcast in stages 9A and 9B,respectively, in a manner similar to that described in stages 12A and12B. The position of the responder UEA 506 may also be determined in amanner similar to that described in stage 12A, e.g., based on positionsof first initiator UEX 502 or second initiator UEY 504 if provided atstages 10A and 10B.

FIG. 6 illustrates an example of a signaling flow 600 for separateranging sessions initiated by a first initiator UEX 602 and a secondinitiator UEY 604 and that include responder UEA and colliding PRSbroadcast times, as discussed herein. The signaling flow 600 is similarto signaling flow 500 shown in FIG. 5 , but the second initiator UEY 604does not reschedule the second ranging session. The initiator UEX 602,initiator UEY 604, and responder UEA 606 may be one or more of thevehicle based UEs (V-UE) 102 and 104, RSU 110 or UE 112, as described inFIG. 1 . It should be understood that FIG. 6 illustrates the signalingfor multiple ranging procedures involving only one responder UE, e.g.,UEA 606, but that additional responder UEs may be present, which wouldinvolve additional communications similar to that shown in FIG. 6 . Asillustrated, the communications between the UEs 602, 604, and 606 inFIG. 6 may be direct communications between the entities and may notinvolve infrastructure devices, such as base stations, to forward themessages between the entities.

At stage 1A, the first initiator UEX 602 sends a pre-PRS message(pre-ranging message) to request a ranging session with responder UEA606. The pre-PRS message may be transmitted via a licensed spectrum. Thepre-PRS message may indicate ranging signal properties to be used by theresponder UEA 606 (as well as the initiator UEX and any other responderUEs) in the ranging session with initiator UEX 602, such as a session IDand PRS resources, including frequency channel and timing instancesincluding the PRS broadcast time and reserved LBT time (or other delaytime), and PRS identifier (ID).

At stage 1B, the second initiator UEY 604 sends a pre-PRS message torequest a ranging session with the responder UEA 606. The pre-PRSmessage of stage 1B is after the pre-PRS message of stage 1A, and thus,the ranging session initiated by the pre-PRS message in stage 1A issometimes referred to as the first ranging sessions and the rangingsession initiated by the pre-PRS message in stage 1B is sometimesreferred to as the second ranging sessions. Similar to stage 1A, thepre-PRS message sent in stage 1B may be transmitted via a licensedspectrum and may indicate ranging signal properties to be used in theranging session by the responder UEA 606 (as well as the initiator UEY604 and any other responder UEs) in the second ranging session withinitiator UEY 604, such as a session ID and PRS resources, includingfrequency channel and timing instances including the PRS broadcast timeand reserved LBT time (or other delay time), and PRS identifier (ID).

At stage 2, the responder UEA 606 determines if a collision existsbetween the first PRS and second PRS assigned respectively in the firstpre-PRS message of stage 1A and the second pre-PRS message of stage 1B.As discussed, e.g., in FIG. 4 , a collision may be determined if the PRSsignals for both ranging sessions are assigned the same frequencychannels and if a second PRS broadcast time is within a predeterminedamount of time (e.g., collision threshold) of the first PRS broadcasttime. The duration of the collision threshold may be predetermined and,in some implementations, may be based on the approximate duration of areserved LBT time (or other delay time), e.g., the collision thresholdmay be a percentage (e.g., 100%, 80%, 60%, etc.) of the reserved LBTtime associated with the first PRS broadcast. Other considerations andfactors may be used to determine the duration of the collisionthreshold. In some implementations, the responder UEA 606 may furtherdetermine the available times for PRS broadcast, as illustrated in FIG.4 . For example, the available times may be determined based on timesbefore the first PRS broadcast time and after the reserved LBT time orafter the collision threshold time.

At stage 3, the responder UEA 606 sends a pre-PRS message (pre-rangingmessage) to the first initiator UEX 602 in response to the pre-PRSrequest of stage 1A, acknowledging the request, thereby indicating thatthe responder UEA 606 accepts the request for the ranging session frominitiator UEX 602. The pre-PRS message of stage 4A may be transmitted ona licensed spectrum.

At stage 4, the responder UEA 606 sends a pre-PRS message (pre-rangingmessage) to the second initiator UEY 604 in response to the pre-PRSrequest of stage 1B. Due to the collision of the second PRS assigned inthe second pre-PRS message of stage 1B with the first PRS assigned inthe first pre-PRS message of stage 1A, the responding pre-PRS message instage 4 includes an indication of a PRS collision, e.g., using a noacknowledgement (NACK) message. In some implementations, the responderUEA 606 may include an indication of available PRS broadcast times inthe pre-PRS message in stage 4. The indication of available PRSbroadcast times, for example, may be the start and end times of theavailable times, the start times and durations of the available times,the first PRS broadcast time and optionally either the reserved LBT timeor collision threshold duration, etc. The pre-PRS message of stage 4 maybe transmitted on a licensed spectrum.

As illustrated in the following, the initiator UEY 604 proceeds with thesecond ranging session without reconstructing the second rangingsessions to avoid the PRS collision by the responder UEA.

At stage 5A, the first initiator UEX 602 broadcasts a PRS signal using aset of PRS resources that were identified in the pre-PRS message ofstage 1A. The PRS signal may be broadcast on an unlicensed spectrum inorder to use a wide frequency band. The first initiator UEX 602 recordsthe ToD of the PRS signal and in some implementations the AoD of the PRSsignal and the responder UEA 606 records the ToA of the PRS signal andin some implementations measures and records the AoA of the PRS signal.

At stage 5B, in response to receiving the PRS signal in stage 5A, theresponder UEA 606 broadcasts a PRS signal using the PRS resources(including frequency channel, PRS broadcast time and reserved LBT time)assigned in the pre-PRS message of stage 1A. The PRS signal may bebroadcast on an unlicensed spectrum in order to use a wide frequencyband. The responder UEA 606 records the ToD of the PRS signal and insome implementations the AoD of the PRS signal and the first initiatorUEX 602 records the ToA of the PRS signal and in some implementationsmeasures and records the AoA of the PRS signal.

At stage 6A, the second initiator UEY 604 broadcasts a PRS signal usinga set of PRS resources that were identified in the pre-PRS message ofstage 1B. The PRS signal may be broadcast on an unlicensed spectrum inorder to use a wide frequency band. The second initiator UEY 604 recordsthe ToD of the PRS signal and in some implementations the AoD of the PRSsignal and the responder UEA 606 records the ToA of the PRS signal andin some implementations measures and records the AoA of the PRS signal.

At stage 6B, as illustrated with the dotted line, the responder UEA 606may broadcast a PRS signal if possible, e.g., if the broadcast times forthe PRS in stage 5B and stage 6B do not in fact collide. For example, ifthe PRS broadcast in stage 5B occurred prior to the scheduled broadcasttime for the second PRS in stage 6B, the responder UEA 606 may broadcastthe PRS signal using the PRS resources (including frequency channel, therevised PRS broadcast time and reserved LBT time) assigned in thepre-PRS message of stage 1B, otherwise, the responder UEA 606 will notbroadcast the PRS signal. The initiator UEY 604, thus, will wait toreceive the broadcast PRS signal. The PRS signal in stage 6B (ifbroadcast) may be broadcast on an unlicensed spectrum in order to use awide frequency band. If the PRS signal is broadcast, the responder UEA606 records the ToD of the PRS signal and in some implementations theAoD of the PRS signal and the second initiator UEY 604 records the ToAof the PRS signal and in some implementations measures and records theAoA of the PRS signal.

At stage 7A, the first initiator UEX 602 sends a post-PRS message to theresponder UEA 606 indicating the ToD, and in some implementations theAoD, of the PRS signal broadcast at stage 5A and indicating the ToA, andin some implementations the AoA, of the PRS signal received at stage 5B.If the position of the first initiator UEX 602 is known, the post-PRSmessage may further include a current position of the first initiatorUEX 602.

At stage 7B, the responder UEA 606 sends a post-PRS message to the firstinitiator UEX 602 indicating the ToA, and in some implementations theAoA, of the PRS signal received at stage 5A and indicating the ToD, andin some implementations the AoD, of the PRS signal broadcast at stage5B. If the position of the responder UEA 606 is known, the post-PRSmessage may further include a current position of the responder UEA 606.

At stage 8A, the second initiator UEY 604 may send a post-PRS message tothe responder UEA 606 indicating the ToD, and in some implementationsthe AoD, of the PRS signal broadcast at stage 6A and indicating whetherthe PRS in stage 6B was received, and if so, the ToA, and in someimplementations the AoA, of the PRS signal received at stage 6B. If theposition of the second initiator UEY 604 is known, the post-PRS messagemay further include a current position of the second initiator UEY 604.

At stage 8B, the responder UEA 606 may send a post-PRS message to thesecond initiator UEY 604 indicating the ToA, and in some implementationsthe AoA, of the PRS signal received at stage 6A and indicating whetherthe PRS in stage 6B was broadcast, and if so, the ToD, and in someimplementations the AoD, of the PRS signal broadcast at stage 6B. If theposition of the responder UEA 606 is known, the post-PRS message mayfurther include a current position of the responder UEA 606.

At stage 9A, the first initiator UEX 602 may determine the range betweenUEX 602 and responder UEA 606 based on the ToD and ToA of the PRSsignals broadcast in stages 5A and 5B. For example, the range may bedetermined based on the ToD_(i) and ToA_(i) for the PRS_(i) signals(where i=1 for PRS broadcast by the initiator UEX 602 and i=2 for PRSbroadcast by the responder UEA 606) as:

$\begin{matrix}{{Range} = {\frac{\left( {{ToD}_{1} - {ToA}_{2}} \right) - \left( {{ToA}_{1} - {ToD}_{2}} \right)}{2c}.}} & {{eq}.3}\end{matrix}$

If the position of the responder UEA 606 is known, e.g., provided inpost-PRS message in stage 7B, along with additional information, such asAoA or AoD of the PRS signals or positions and ranges for otherresponder UEs (not shown in FIG. 6 ), or geographic information, such asstreet locations, the position of the initiator UEX 602 may bedetermined using, e.g., multilateration and constraints pursuant to theAoA or AoD of the PRS signals and geographic information.

At stage 9B, as indicated by the dotted lines, if the responder UEAbroadcast the PRS in stage 6B, the second initiator UEY 604 maydetermine the range between UEY 604 and responder UEA 606 based on theToD and ToA of the PRS signals broadcast in stages 6A and 6B, in amanner similar to that described in stage 9A. The position of theinitiator UEY 604 may also be determined in a manner similar to thatdescribed in stage 9A. If the responder UEA 60 did not broadcast the PRSin stage 6B, the range between UEY 604 and responder UEA 606 is notdetermined, and the position of the second initiator UEY 604 would needto be determined without use of the range to the responder UEA 606.

At stage 9C, the responder UEA 606 may determine the range between UEA606 and the first initiator UEX 602 and, if the if the responder UEAbroadcast the PRS in stage 6B, the range between UEA 606 and secondinitiator UEY 604, based on the ToA and ToD of the PRS signals broadcastin stages 5A and 5B and broadcast in stages 6A and 6B, respectively, ina manner similar to that described in stages 9A and 9B. The position ofthe responder UEA 606 may also be determined in a manner similar to thatdescribed in stage 9A, e.g., based on positions of first initiator UEX602 or second initiator UEY 604 if provided at stages 7A and 7B. If theresponder UEA 606 did not broadcast the PRS in stage 6B, the rangebetween responder UEA 606 and the second initiator UEY 604 is notdetermined, and the position of the responder UEA 606 would need to bedetermined without use of the range to the second initiator UEY 604.

FIG. 7 shows a schematic block diagram illustrating certain exemplaryfeatures of a user equipment (UE) 700, which may be UE in vehicles 102or 104, an RSU 110, or UE 112 held by a pedestrian 114, as illustratedin FIG. 1 . The UE 700 may be configured to act as an initiator UE,e.g., UEY, or a responder UE, e.g., UEA during ranging sessions, asdiscussed herein. If the UE 700 is a V-UE, it may be configured tocontrol the automated driving of a vehicle, e.g., vehicle 102. Forexample, the UE 700 may include a vehicle interface 705 with whichcommands are provided to the vehicle for automated driving and sensoryinput, including speed and acceleration, may be provided from thevehicle to UE 700. The UE 700 may, for example, include one or moreprocessors 702, memory 704, an inertial measurement unit (IMU) 707 thatmay include, e.g., an accelerometer, gyroscope, magnetometers, etc.,which may be used to detect orientation with respect to a global orlocal reference frame and the motion or one or more motioncharacteristics of the vehicle, a satellite positioning system (SPS)receiver 709 to determine, e.g., a GPS position, and an externalinterface including, e.g., a Wireless Wide Area Network (WWAN)transceiver 710, and a Wireless Local Area Network (WLAN) transceiver714, which may be operatively coupled with one or more connections 706(e.g., buses, lines, fibers, links, etc.) to non-transitory computerreadable medium 720 and memory 704. The UE 700 may further includeadditional items, which are not shown, such as a user interface that mayinclude e.g., a display, a keypad or other input device, such as virtualkeypad on the display, through which a user may interface with the userdevice. In certain example implementations, all or part of UE 700 maytake the form of a chipset, and/or the like.

Transceiver 710 may be, e.g., a cellular transceiver, that is configuredto transmit and receive direct communications in the wireless network,as illustrated in FIG. 1 . The transceiver 710 may include a transmitter711 enabled to transmit one or more signals over one or more types ofwireless communication networks and a receiver 712 to receive one ormore signals transmitted over the one or more types of wirelesscommunication networks. Transceiver 714 may be, e.g., a short-rangetransceiver, and may be configured to transmit and receive directcommunications in the wireless network, as illustrated in FIG. 1 . Thetransceiver 714 may include a transmitter 715 enabled to transmit one ormore signals, including ranging signals (PRS signals) and pre-ranging(pre-PRS) and post-ranging (post-PRS) messages, and combine and separatemessages, over one or more types of wireless communication networks anda receiver 716 to receive one or more signals, e.g., including PRS andpre-PRS and post-PRS messages, combine and separate messages,transmitted over the one or more types of wireless communicationnetworks. The transceivers 710 and 714 enable the UE 700 to communicatewith transportation entities using D2D communication links, such asDSRC, C-V2X, or 5G NR.

In some embodiments, UE 700 may include antenna 709, which may beinternal or external. The antenna 709 may be used to transmit and/orreceive signals processed by transceiver 710 and/or transceiver 714. Insome embodiments, antenna 709 may be coupled to transceiver 710 and/ortransceiver 714. In some embodiments, measurements of signals received(transmitted) by UE 700 may be performed at the point of connection ofthe antenna 709 and transceiver 710 and/or transceiver 714. For example,the measurement point of reference for received (transmitted) RF signalmeasurements may be an input (output) terminal of the receivers 712, 716(transmitters 711, 715) and an output (input) terminal of the antenna709. In a UE 700 with multiple antennas 709 or antenna arrays, theantenna connector may be viewed as a virtual point representing theaggregate output (input) of multiple antennas. The phase difference ofreceived signals at multiple antennas or antenna array may be used todetermine the AoA of the signal with respect to the antenna array, whichmay be converted to a local or global reference frame based on a knownorientation of the UE 700, e.g., based on the orientation of the UE 700to the global or local reference frame as measured by the IMU 707.

The one or more processors 702 may be implemented using a combination ofhardware, firmware, and software. For example, the one or moreprocessors 702 may be configured to perform the functions discussedherein by implementing one or more instructions or program code 708 on anon-transitory computer readable medium, such as medium 720 and/ormemory 704. In some embodiments, the one or more processors 702 mayrepresent one or more circuits configurable to perform at least aportion of a data signal computing procedure or process related to theoperation of UE 700.

The medium 720 and/or memory 704 may store instructions or program code708 that contain executable code or software instructions that whenexecuted by the one or more processors 702 cause the one or moreprocessors 702 to operate as a special purpose computer programmed toperform the techniques disclosed herein. As illustrated in UE 700, themedium 720 and/or memory 704 may include one or more components ormodules that may be implemented by the one or more processors 702 toperform the methodologies described herein. While the components ormodules are illustrated as software in medium 720 that is executable bythe one or more processors 702, it should be understood that thecomponents or modules may be stored in memory 704 or may be dedicatedhardware either in the one or more processors 702 or off the processors.

A number of software modules and data tables may reside in the medium720 and/or memory 704 and be utilized by the one or more processors 702in order to manage both communications and the functionality describedherein. It should be appreciated that the organization of the contentsof the medium 720 and/or memory 704 as shown in UE 700 is merelyexemplary, and as such the functionality of the modules and/or datastructures may be combined, separated, and/or be structured in differentways depending upon the implementation of the UE 700.

The medium 720 and/or memory 704 may include a ranging module 721 thatwhen implemented by the one or more processors 702 configures the one ormore processors 702 to participate in a ranging session as an initiatorUE or a responder UE as discussed herein. The ranging module 721, forexample, may include a pre-ranging module (pre-PRS message module 722),a ranging signal module (PRS module 724), a post-ranging module(post-PRS message module 726), and a range module 728.

The medium 720 and/or memory 704 may include a pre-PRS message module722 that when implemented by the one or more processors 702 configuresthe one or more processors 702 to generate and transmit or receivepre-ranging messages, such as pre-PRS messages, via the transceiver 714,e.g., to initiate a ranging session or to accept a ranging session. Thepre-PRS messages may be broadcast, multicast, or unicast (with RRCconnection). In some implementations, the PRS messages may betransmitted and received over a licensed spectrum. The pre-PRS messagemay be an initiating pre-PRS message to initiate a ranging session or aresponding pre-PRS message to acknowledge an initiating pre-PRS messageor to indicate the presence of a PRS collision with another rangingsession, e.g., with a no acknowledge (NACK) message. The pre-PRSmessages may include identifiers for the initiating UE and one or moreresponder UEs for the positioning session, which may be monitored by theUE 700 over a plurality of ranging sessions. The participating UEs maybe determined, e.g., from capabilities messages received by the UE 700or from monitoring pre-PRS messages broadcast by multiple initiator UEsover a period of time. The pre-PRS messages may include a session ID,and ranging signal resources for participating UE, including a time andfrequencies for responder UEs to broadcast ranging (PRS) signal in theranging session, PRS ID, etc. The time resource, for example, may be aPRS broadcast time and reserved LBT time (e.g., maximum LBT time) oranother delay time. A responding pre-PRS message from a responder UEthat indicates the presence of a PRS collision with another rangingsession may further include available PRS broadcast times.

The medium 720 and/or memory 704 may include a PRS module 724 that whenimplemented by the one or more processors 702 configures the one or moreprocessors 702 to broadcast and receive a ranging signal to and fromother UEs in the ranging session, via the transceiver 714, as discussedherein. The ranging signal, for example, may be a PRS signal, such as aQuadrature Phase Shift Keying (QPSK) modulated pseudo-noise (PN)sequence as discussed herein. The ranging signal may be broadcast at theassigned broadcast time, e.g., after a LBT procedure using the reservedLBT time, and with the PRS identifier and at the frequencies indicatedover the pre-PRS message. The ranging signal may be broadcast andreceived over unlicensed spectrum and may be broadcast pursuant tocategory 2 or category 4 LBT constraints. The one or more processors702, for example, may be configured to measure the ToD of broadcastranging signals and the ToA of received ranging signals, and may beconfigured to measure the AoD of broadcast ranging signals and the AoAof received ranging signals.

The medium 720 and/or memory 704 may include a post-PRS message module726 that when implemented by the one or more processors 702 configuresthe one or more processors 702 to send and receive post-ranging messagesto and from other UEs in the ranging session, via the transceiver 714,as discussed herein. The post-PRS messages that may include, e.g., anindication of the ToD, and in some implementations the AoD, of thebroadcast ranging signals and an indication of the ToA, and in someimplementations the AoA, of the received ranging signals. In someimplementation, the indication of the ToD and ToA may be a differencebetween the ToD and ToA. In some implementations, the post-PRS messagesmay include an indication of the position of the UE, e.g., if the UE isan anchor UE used for positioning another UE.

The medium 720 and/or memory 704 may include a range module 728 thatwhen implemented by the one or more processors 702 configures the one ormore processors 702 to determine a range to other UEs based on the ToDand ToA of broadcast and received ranging signals as measured by the UE700 and received in the post-PRS messages from other UEs.

The medium 720 and/or memory 704 may include a position module 730 thatwhen implemented by the one or more processors 702 configures the one ormore processors 702 to determine a position for the UE 700, e.g., basedon one or more ranges to broadcasting UEs and their location informationusing multilateration or other appropriate techniques discussed herein.For example, the one or more processors 702 may implement a Kalmanfilter or Extended Kalman filter to determine the position of the UE700.

The medium 720 and/or memory 704 may include a collision module 732 thatwhen implemented by the one or more processors 702 configures the one ormore processors 702 to determine if there is a PRS collision in multipleranging sessions. The collision may be determined based on PRS for twoseparate ranging sessions using the same time and frequency resources.For example, the one or more processors 702 may be configured to thepresence of a collision between a first PRS signal and a second PRSsignal if the time to broadcast the second PRS signal is within apredetermined amount of time from the time to broadcast the first PRSsignal. The predetermined amount of time, for example, may be apredetermined maximum wait time for a LBT procedure or a predeterminedcollision threshold time, e.g., as discussed in FIG. 4 .

The medium 720 and/or memory 704 may include an available broadcast time734 that when implemented by the one or more processors 702 configuresthe one or more processors 702 to determine an available time for theresponder UE to broadcast PRS when a PRS collision has been detected.For example, when a collision between a first PRS signal and a secondPRS signal has been detected, the available time to broadcast the secondPRS signal may be determined based on the time to broadcast the firstPRS signal. The available time to broadcast, for example, may bedetermined based on a predetermined maximum wait time for a LBTprocedure or based on a predetermined collision threshold time, e.g., asdiscussed in FIG. 4 . If the UE 700 is the initiator UE, the one or moreprocessors 702 may be configured to determine the available time tobroadcast the PRS by a responder UE based on an available time tobroadcast received from the responder UE in the pre-PRS message. If theavailable time to broadcast is not received from the responder UE, theone or more processors 702 may be configured to determine the availabletime to broadcast the PRS by a responder UE based on the initialbroadcast time for the PRS signal and a predetermined time period. Thepredetermined time period, for example, may be based on a maximum waittime for a LBT procedure for broadcasting the PRS signal or apredetermined collision threshold time period.

The methodologies described herein may be implemented by various meansdepending upon the application. For example, these methodologies may beimplemented in hardware, firmware, software, or any combination thereof.For a hardware implementation, the one or more processors 702 may beimplemented within one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, micro-controllers,microprocessors, electronic devices, other electronic units designed toperform the functions described herein, or a combination thereof.

For a firmware and/or software implementation, the methodologies may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. Any machine readable mediumtangibly embodying instructions may be used in implementing themethodologies described herein. For example, software codes may bestored in a non-transitory computer readable medium 720 or memory 704that is connected to and executed by the one or more processors 702.Memory may be implemented within the one or more processors or externalto the one or more processors. As used herein the term “memory” refersto any type of long term, short term, volatile, nonvolatile, or othermemory and is not to be limited to any particular type of memory ornumber of memories, or type of media upon which memory is stored.

If implemented in firmware and/or software, the functions may be storedas one or more instructions or program code 708 on a non-transitorycomputer readable medium, such as medium 720 and/or memory 704. Examplesinclude computer readable media encoded with a data structure andcomputer readable media encoded with a computer program 708. Forexample, the non-transitory computer readable medium including programcode 708 stored thereon may include program code 708 to support multipleranging sessions including determining the presence of a PRS collisionand to provide an indication of such to an initiator UE, which mayinitiate a new ranging session based on the available PRS broadcast timefor the responder UE, in a manner consistent with disclosed embodiments.Non-transitory computer readable medium 720 includes physical computerstorage media. A storage medium may be any available medium that can beaccessed by a computer. By way of example, and not limitation, suchnon-transitory computer readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to storedesired program code 708 in the form of instructions or data structuresand that can be accessed by a computer; disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer readable media.

In addition to storage on computer readable medium 720, instructionsand/or data may be provided as signals on transmission media included ina communication apparatus. For example, a communication apparatus mayinclude a transceiver 710 having signals indicative of instructions anddata. The instructions and data are configured to cause one or moreprocessors to implement the functions outlined in the claims. That is,the communication apparatus includes transmission media with signalsindicative of information to perform disclosed functions.

Memory 704 may represent any data storage mechanism. Memory 704 mayinclude, for example, a primary memory and/or a secondary memory.Primary memory may include, for example, a random-access memory, readonly memory, etc. While illustrated in this example as being separatefrom one or more processors 702, it should be understood that all orpart of a primary memory may be provided within or otherwiseco-located/coupled with the one or more processors 702. Secondary memorymay include, for example, the same or similar type of memory as primarymemory and/or one or more data storage devices or systems, such as, forexample, a disk drive, an optical disc drive, a tape drive, asolid-state memory drive, etc.

In certain implementations, secondary memory may be operativelyreceptive of, or otherwise configurable to couple to a non-transitorycomputer readable medium 720. As such, in certain exampleimplementations, the methods and/or apparatuses presented herein maytake the form in whole or part of a computer readable medium 720 thatmay include computer implementable code 708 stored thereon, which ifexecuted by one or more processors 702 may be operatively enabled toperform all or portions of the example operations as described herein.Computer readable medium 720 may be a part of memory 704.

FIG. 8 is a flow chart 800 illustrating a method of ranging in adistributed system of user equipment (UE) performed by a responder UE,such as UEA in FIGS. 3, 5, 6 , or UE 700 in FIG. 7 .

At block 802, the responder UE receives a first pre-ranging requestmessage from a first initiator UE to initiate a first ranging session,the first pre-ranging request message comprising first ranging signalresources including a time and frequencies for the responder UE tobroadcast a first ranging signal in the first ranging session, e.g., asdiscussed at stage 1A in FIGS. 5 and 6 . A means for receiving a firstpre-ranging request message from a first initiator UE to initiate afirst ranging session, the first pre-ranging request message comprisingfirst ranging signal resources including a time and frequencies for theresponder UE to broadcast a first ranging signal in the first rangingsession may be, e.g., the transceiver 714 and the one or more processors702 with dedicated hardware or implementing executable code or softwareinstructions in memory 704 and/or medium 720, such as the ranging module721 and the pre-PRS message module 722.

At block 804, the responder UE receives a second pre-ranging requestmessage from a second initiator UE to initiate a second ranging session,the second pre-ranging request message comprising second ranging signalresources including a time and frequencies for the responder UE tobroadcast a second ranging signal in the second ranging session, e.g.,as discussed at stage 1B in FIGS. 5 and 6 . A means for receiving asecond pre-ranging request message from a second initiator UE toinitiate a second ranging session, the second pre-ranging requestmessage comprising second ranging signal resources including a time andfrequencies for the responder UE to broadcast a second ranging signal inthe second ranging session may be, e.g., the transceiver 714 and the oneor more processors 702 with dedicated hardware or implementingexecutable code or software instructions in memory 704 and/or medium720, such as the ranging module 721 and the pre-PRS message module 722.

At block 806, the responder UE determines a collision between the firstranging signal and the second ranging signal based on the first rangingsignal resources and the second ranging resources, e.g., as discussed atstage 2 in FIGS. 5 and 6 . A means for determining a collision betweenthe first ranging signal and the second ranging signal based on thefirst ranging signal resources and the second ranging resources may be,e.g., the one or more processors 702 with dedicated hardware orimplementing executable code or software instructions in memory 704and/or medium 720, such as the collision module 732.

At block 808, the responder UE sends a first pre-ranging responsemessage to the first initiator UE acknowledging the first pre-rangingrequest message, e.g., as discussed at stage 3 in FIGS. 5 and 6 . Ameans for sending a first pre-ranging response message to the firstinitiator UE acknowledging the first pre-ranging request message may be,e.g., the transceiver 714 and the one or more processors 702 withdedicated hardware or implementing executable code or softwareinstructions in memory 704 and/or medium 720, such as the ranging module721 and the pre-PRS message module 722.

At block 810, the responder UE sends a second pre-ranging responsemessage to the second initiator UE indicating the collision with thesecond ranging signal resources for the second ranging signal, e.g., asdiscussed at stage 4 in FIGS. 5 and 6 . A means for sending a secondpre-ranging response message to the second initiator UE indicating thecollision with the second ranging signal resources for the secondranging signal may be, e.g., the transceiver 714 and the one or moreprocessors 702 with dedicated hardware or implementing executable codeor software instructions in memory 704 and/or medium 720, such as theranging module 721 and the pre-PRS message module 722 and the collisionmodule 732.

By way of example, in some implementations, the responder UE maydetermine the collision between the first ranging signal and the secondranging signal by determining that the time to broadcast the secondranging signal is within a predetermined amount of time of the time tobroadcast the first ranging signal, e.g., as discussed in FIG. 4 and atstage 2 of FIGS. 5 and 6 . For example, the predetermined amount of timemay be a predetermined maximum wait time for a listen-before-transmitprocedure for broadcasting the second ranging signal. In anotherexample, the predetermined amount of time may be a predeterminedcollision threshold time. A means for determining that the time tobroadcast the second ranging signal is within a predetermined amount oftime of the time to broadcast the first ranging signal may be, e.g., theone or more processors 702 with dedicated hardware or implementingexecutable code or software instructions in memory 704 and/or medium720, such as the collision module 732. Additionally, the responder UEmay determine the collision between the first ranging signal and thesecond ranging signal by determining that the frequencies to broadcastthe second ranging signal and the frequencies to broadcast the firstranging signal are the same, signal, e.g., as discussed in FIG. 4 and atstage 2 of FIGS. 5 and 6 . A means for determining that the frequenciesto broadcast the second ranging signal and the frequencies to broadcastthe first ranging signal are the same may be, e.g., the one or moreprocessors 702 with dedicated hardware or implementing executable codeor software instructions in memory 704 and/or medium 720, such as thecollision module 732.

In some implementations, the responder UE may further determine anavailable time to broadcast the second ranging signal, wherein thesecond pre-ranging response message includes the available time tobroadcast the second ranging signal, e.g., as discussed in FIG. 4 and atstage 2 of FIGS. 5 and 6 . The available time to broadcast the secondranging signal may be based on the time to broadcast the first rangingsignal included in the first ranging signal resources. In one example,the available time to broadcast the second ranging signal may be furtherbased on a predetermined maximum wait time for a listen-before-transmitprocedure for broadcasting the first ranging signal. In another example,the available time to broadcast the second ranging signal may be furtherbased on a predetermined collision threshold time A means fordetermining an available time to broadcast the second ranging signal,wherein the second pre-ranging response message includes the availabletime to broadcast the second ranging signal may be, e.g., the one ormore processors 702 with dedicated hardware or implementing executablecode or software instructions in memory 704 and/or medium 720, such asthe available broadcast time module 734.

In one implementation, the responder UE may receive a third pre-rangingrequest message from the second initiator UE to initiate the secondranging session, the third pre-ranging request message comprising thirdranging signal resources including a time and frequencies for theresponder UE to broadcast the second ranging signal in the secondranging session, e.g., as discussed at stage 6 in FIG. 5 . A means forreceiving a third pre-ranging request message from the second initiatorUE to initiate the second ranging session, the third pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the second ranging signalin the second ranging session may be, e.g., the transceiver 714 and theone or more processors 702 with dedicated hardware or implementingexecutable code or software instructions in memory 704 and/or medium720, such as the ranging module 721 and the pre-PRS message module 722.The responder UE may perform the first ranging session with the firstinitiator UE comprising broadcasting the first ranging signal accordingto the first ranging signal resources, e.g., as discussed at stage 8B inFIG. 5 , and may perform the second ranging session with the secondinitiator UE comprising broadcasting the second ranging signal accordingto the third ranging signal resources, e.g., as discussed at stage 9B inFIG. 5 . A means for performing the first ranging session with the firstinitiator UE comprising broadcasting the first ranging signal accordingto the first ranging signal resources, and a means for performing thesecond ranging session with the second initiator UE comprisingbroadcasting the second ranging signal according to the third rangingsignal resources may be, e.g., the transceiver 714 and the one or moreprocessors 702 with dedicated hardware or implementing executable codeor software instructions in memory 704 and/or medium 720, such as theranging module 721 and the PRS module 724.

FIG. 9 is a flow chart 900 illustrating a method of ranging in adistributed system of user equipment (UE) performed by an initiator UE,such as UEY in FIGS. 3, 5, 6 , or UE 700 in FIG. 7 .

At block 902, the initiator UE transmits a first pre-ranging requestmessage to a responder UE to initiate a first ranging session, the firstpre-ranging request message comprising first ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast afirst ranging signal in the first ranging session, e.g., as discussed atstage 1B in FIGS. 5 and 6 . A means for transmitting a first pre-rangingrequest message to a responder UE to initiate a first ranging session,the first pre-ranging request message comprising first ranging signalresources including a time and frequencies for the responder UE tobroadcast a first ranging signal in the first ranging session may be,e.g., the transceiver 714 and the one or more processors 702 withdedicated hardware or implementing executable code or softwareinstructions in memory 704 and/or medium 720, such as the ranging module721 and the pre-PRS message module 722.

At block 904, the initiator UE receives a first pre-ranging responsemessage from the responder UE indicating a collision between the firstranging signal resources for the first ranging signal and second rangingsignal resources for a second ranging signal for a second initiator UE,e.g., as discussed at stage 4 in FIGS. 5 and 6 . A means for receiving afirst pre-ranging response message from the responder UE indicating acollision between the first ranging signal resources for the firstranging signal and second ranging signal resources for a second rangingsignal for a second initiator UE may be, e.g., the transceiver 714 andthe one or more processors 702 with dedicated hardware or implementingexecutable code or software instructions in memory 704 and/or medium720, such as the ranging module 721 and the pre-PRS message module 722.

In some implementations, the initiator UE may further determine anavailable time for the responder UE to broadcast the first rangingsignal, e.g., as discussed in FIG. 4 and at stage 5 of FIG. 5 . Forexample, the first pre-ranging response message may comprise theavailable time for the responder UE to broadcast the first rangingsignal. In another example, the available time for the responder UE tobroadcast the first ranging signal may be determined based on the timeto broadcast the first ranging signal included in the first rangingsignal resources and a predetermined time period. The predetermined timeperiod, for example, may be based on a maximum wait time for alisten-before-transmit procedure for broadcasting the first rangingsignal or a predetermined collision threshold time period. A means fordetermining an available time for the responder UE to broadcast thefirst ranging signal may be, e.g., the one or more processors 702 withdedicated hardware or implementing executable code or softwareinstructions in memory 704 and/or medium 720, such as the availablebroadcast time module 734. The initiator UE may transmit a secondpre-ranging request message to the responder UE to initiate the firstranging session, the second pre-ranging request message comprising thirdranging signal resources including a time and frequencies for theresponder UE to broadcast the first ranging signal in the first rangingsession based on the available time, e.g., as discussed at stage 6 ofFIG. 5 . A means for transmitting a second pre-ranging request messageto the responder UE to initiate the first ranging session, the secondpre-ranging request message comprising third ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast thefirst ranging signal in the first ranging session based on the availabletime may be, e.g., the one or more processors 702 with dedicatedhardware or implementing executable code or software instructions inmemory 704 and/or medium 720, such as the ranging module 721 and thepre-PRS message module 722.

In some implementations, the initiator UE may further receive a secondpre-ranging response message from the responder UE acknowledging thesecond pre-ranging request message, e.g., as discussed at stage 7 ofFIG. 5 , and may perform the first ranging session with responder UEcomprising receiving the first ranging signal transmitted by theresponder UE according to the third ranging signal resources, e.g., asdiscussed at stage 9B of FIG. 5 . A means for receiving a secondpre-ranging response message from the responder UE acknowledging thesecond pre-ranging request message may be, e.g., the transceiver 714 andthe one or more processors 702 with dedicated hardware or implementingexecutable code or software instructions in memory 704 and/or medium720, such as the ranging module 721 and the pre-PRS message module 722.A means for performing the first ranging session with responder UEcomprising receiving the first ranging signal transmitted by theresponder UE according to the third ranging signal resources may be,e.g., the transceiver 714 and the one or more processors 702 withdedicated hardware or implementing executable code or softwareinstructions in memory 704 and/or medium 720, such as the ranging module721 and the PRS module 724.

In some implementations, the initiator UE may perform the first rangingsession with responder UE by transmitting an initial ranging signal andwaiting to receive the first ranging signal transmitted by the responderUE according to the first ranging signal resources, e.g., as discussedat stages 6A and 6B in FIG. 6 . A means for performing the first rangingsession with responder UE comprising transmitting an initial rangingsignal and waiting to receive the first ranging signal transmitted bythe responder UE according to the first ranging signal resources may be,e.g., the transceiver 714 and the one or more processors 702 withdedicated hardware or implementing executable code or softwareinstructions in memory 704 and/or medium 720, such as the ranging module721 and the PRS module 724.

Reference throughout this specification to “one example”, “an example”,“certain examples”, or “exemplary implementation” means that aparticular feature, structure, or characteristic described in connectionwith the feature and/or example may be included in at least one featureand/or example of claimed subject matter. Thus, the appearances of thephrase “in one example”, “an example”, “in certain examples” or “incertain implementations” or other like phrases in various placesthroughout this specification are not necessarily all referring to thesame feature, example, and/or limitation. Furthermore, the particularfeatures, structures, or characteristics may be combined in one or moreexamples and/or features.

Some portions of the detailed description included herein are presentedin terms of algorithms or symbolic representations of operations onbinary digital signals stored within a memory of a specific apparatus orspecial purpose computing device or platform. In the context of thisparticular specification, the term specific apparatus or the likeincludes a general-purpose computer once it is programmed to performparticular operations pursuant to instructions from program software.Algorithmic descriptions or symbolic representations are examples oftechniques used by those of ordinary skill in the signal processing orrelated arts to convey the substance of their work to others skilled inthe art. An algorithm is here, and generally, is considered to be aself-consistent sequence of operations or similar signal processingleading to a desired result. In this context, operations or processinginvolve physical manipulation of physical quantities. Typically,although not necessarily, such quantities may take the form ofelectrical or magnetic signals capable of being stored, transferred,combined, compared, or otherwise manipulated. It has proven convenientat times, principally for reasons of common usage, to refer to suchsignals as bits, data, values, elements, symbols, characters, terms,numbers, numerals, or the like. It should be understood, however, thatall of these or similar terms are to be associated with appropriatephysical quantities and are merely convenient labels. Unlessspecifically stated otherwise, as apparent from the discussion herein,it is appreciated that throughout this specification discussionsutilizing terms such as “processing,” “computing,” “calculating,”“determining” or the like refer to actions or processes of a specificapparatus, such as a special purpose computer, special purpose computingapparatus or a similar special purpose electronic computing device. Inthe context of this specification, therefore, a special purpose computeror a similar special purpose electronic computing device is capable ofmanipulating or transforming signals, typically represented as physicalelectronic or magnetic quantities within memories, registers, or otherinformation storage devices, transmission devices, or display devices ofthe special purpose computer or similar special purpose electroniccomputing device.

In the preceding detailed description, numerous specific details havebeen set forth to provide a thorough understanding of claimed subjectmatter. However, it will be understood by those skilled in the art thatclaimed subject matter may be practiced without these specific details.In other instances, methods and apparatuses that would be known by oneof ordinary skill have not been described in detail so as not to obscureclaimed subject matter.

The terms, “and”, “or”, and “and/or” as used herein may include avariety of meanings that also are expected to depend at least in partupon the context in which such terms are used. Typically, “or” if usedto associate a list, such as A, B or C, is intended to mean A, B, and C,here used in the inclusive sense, as well as A, B or C, here used in theexclusive sense. In addition, the term “one or more” as used herein maybe used to describe any feature, structure, or characteristic in thesingular or may be used to describe a plurality or some othercombination of features, structures, or characteristics. Though, itshould be noted that this is merely an illustrative example and claimedsubject matter is not limited to this example.

While there has been illustrated and described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the art that various other modifications may be made, andequivalents may be substituted, without departing from claimed subjectmatter. Additionally, many modifications may be made to adapt aparticular situation to the teachings of claimed subject matter withoutdeparting from the central concept described herein.

Implementation examples are described in the following numbered clauses:

1. A method of ranging between user equipments (UEs) performed by aresponder UE, the method comprising:

receiving a first pre-ranging request message from a first initiator UEto initiate a first ranging session, the first pre-ranging requestmessage comprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session;

receiving a second pre-ranging request message from a second initiatorUE to initiate a second ranging session, the second pre-ranging requestmessage comprising second ranging signal resources including a time andfrequencies for the responder UE to broadcast a second ranging signal inthe second ranging session;

determining a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources;

sending a first pre-ranging response message to the first initiator UEacknowledging the first pre-ranging request message; and

sending a second pre-ranging response message to the second initiator UEindicating the collision with the second ranging signal resources forthe second ranging signal.

2. The method of clause 1, wherein determining the collision between thefirst ranging signal and the second ranging signal comprises determiningthat the time to broadcast the second ranging signal is within apredetermined amount of time of the time to broadcast the first rangingsignal.

3. The method of clause 2, wherein the predetermined amount of time is apredetermined maximum wait time for a listen-before-transmit procedurefor broadcasting the second ranging signal.

4. The method of clause 2, wherein the predetermined amount of time is apredetermined collision threshold time.

5. The method of any of clauses 2-4, wherein determining the collisionbetween the first ranging signal and the second ranging signal comprisesdetermining that the frequencies to broadcast the second ranging signaland the frequencies to broadcast the first ranging signal are the same.

6. The method of any of clauses 1-5, further comprising determining anavailable time to broadcast the second ranging signal, wherein thesecond pre-ranging response message includes the available time tobroadcast the second ranging signal.

7. The method of clause 6, wherein the available time to broadcast thesecond ranging signal is based on the time to broadcast the firstranging signal included in the first ranging signal resources.

8. The method of clause 7, wherein the available time to broadcast thesecond ranging signal is further based on a predetermined maximum waittime for a listen-before-transmit procedure for broadcasting the firstranging signal.

9. The method of clause 7, wherein the available time to broadcast thesecond ranging signal is further based on a predetermined collisionthreshold time.

10. The method of any of clauses 1-9, further comprising receiving athird pre-ranging request message from the second initiator UE toinitiate the second ranging session, the third pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the second ranging signalin the second ranging session.

11. The method of clause 10, further comprising:

performing the first ranging session with the first initiator UEcomprising broadcasting the first ranging signal according to the firstranging signal resources; and

performing the second ranging session with the second initiator UEcomprising broadcasting the second ranging signal according to the thirdranging signal resources.

12. A responder user equipment configured for ranging between UEs, theresponder UE comprising:

a wireless transceiver configured to wirelessly communicate withentities in a wireless network;

at least one memory; and

at least one processor coupled to the wireless transceiver and the atleast one memory, wherein the at least one processor is configured to:

receive a first pre-ranging request message from a first initiator UE toinitiate a first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session;

receive a second pre-ranging request message from a second initiator UEto initiate a second ranging session, the second pre-ranging requestmessage comprising second ranging signal resources including a time andfrequencies for the responder UE to broadcast a second ranging signal inthe second ranging session;

determine a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources;

send a first pre-ranging response message to the first initiator UEacknowledging the first pre-ranging request message; and

send a second pre-ranging response message to the second initiator UEindicating the collision with the second ranging signal resources forthe second ranging signal.

13. The responder UE of clause 12, wherein the at least one processor isconfigured to determine the collision between the first ranging signaland the second ranging signal by being configured to determine that thetime to broadcast the second ranging signal is within a predeterminedamount of time of the time to broadcast the first ranging signal.

14. The responder UE of clause 13, wherein the predetermined amount oftime is a predetermined maximum wait time for a listen-before-transmitprocedure for broadcasting the second ranging signal.

15. The responder UE of clause 13, wherein the predetermined amount oftime is a predetermined collision threshold time.

16. The responder UE of any of clauses 13-15, wherein the at least oneprocessor is configured to determine the collision between the firstranging signal and the second ranging signal by being configured todetermine that the frequencies to broadcast the second ranging signaland the frequencies to broadcast the first ranging signal are the same.

17. The responder UE of any of clauses 12-16, wherein the at least oneprocessor is further configured to determine an available time tobroadcast the second ranging signal, wherein the second pre-rangingresponse message includes the available time to broadcast the secondranging signal.

18. The responder UE of clause 17, wherein the available time tobroadcast the second ranging signal is based on the time to broadcastthe first ranging signal included in the first ranging signal resources.

19. The responder UE of clause 18, wherein the available time tobroadcast the second ranging signal is further based on a predeterminedmaximum wait time for a listen-before-transmit procedure forbroadcasting the first ranging signal.

20. The responder UE of clause 18, wherein the available time tobroadcast the second ranging signal is further based on a predeterminedcollision threshold time.

21. The responder UE of any of clauses 12-20, wherein the at least oneprocessor is further configured to receive a third pre-ranging requestmessage from the second initiator UE to initiate the second rangingsession, the third pre-ranging request message comprising third rangingsignal resources including a time and frequencies for the responder UEto broadcast the second ranging signal in the second ranging session.

22. The responder UE of clause 21, wherein the at least one processor isfurther configured to:

perform the first ranging session with the first initiator UE by beingconfigured to broadcast the first ranging signal according to the firstranging signal resources; and

perform the second ranging session with the second initiator UE by beingconfigured to broadcast the second ranging signal according to the thirdranging signal resources.

23. A responder user equipment configured for ranging between UEs, theresponder UE comprising:

means for receiving a first pre-ranging request message from a firstinitiator UE to initiate a first ranging session, the first pre-rangingrequest message comprising first ranging signal resources including atime and frequencies for the responder UE to broadcast a first rangingsignal in the first ranging session;

means for receiving a second pre-ranging request message from a secondinitiator UE to initiate a second ranging session, the secondpre-ranging request message comprising second ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast asecond ranging signal in the second ranging session;

means for determining a collision between the first ranging signal andthe second ranging signal based on the first ranging signal resourcesand the second ranging resources;

means for sending a first pre-ranging response message to the firstinitiator UE acknowledging the first pre-ranging request message; and

means for sending a second pre-ranging response message to the secondinitiator UE indicating the collision with the second ranging signalresources for the second ranging signal.

24. The responder UE of clause 23, wherein the means for determining thecollision between the first ranging signal and the second ranging signalmeans for determining that the time to broadcast the second rangingsignal is within a predetermined amount of time of the time to broadcastthe first ranging signal.

25. The responder UE of clause 24, wherein the predetermined amount oftime is a predetermined maximum wait time for a listen-before-transmitprocedure for broadcasting the second ranging signal.

26. The responder UE of clause 24, wherein the predetermined amount oftime is a predetermined collision threshold time.

27. The responder UE of any of clauses 24-26, wherein means fordetermining the collision between the first ranging signal and thesecond ranging signal means for determining that the frequencies tobroadcast the second ranging signal and the frequencies to broadcast thefirst ranging signal are the same.

28. The responder UE of any of clauses 23-27, further comprising meansfor determining an available time to broadcast the second rangingsignal, wherein the second pre-ranging response message includes theavailable time to broadcast the second ranging signal.

29. The responder UE of clause 28, wherein the available time tobroadcast the second ranging signal is based on the time to broadcastthe first ranging signal included in the first ranging signal resources.

30. The responder UE of clause 29, wherein the available time tobroadcast the second ranging signal is further based on a predeterminedmaximum wait time for a listen-before-transmit procedure forbroadcasting the first ranging signal.

31. The responder UE of clause 29, wherein the available time tobroadcast the second ranging signal is further based on a predeterminedcollision threshold time.

32. The responder UE of any of clauses 23-31, further comprising meansfor receiving a third pre-ranging request message from the secondinitiator UE to initiate the second ranging session, the thirdpre-ranging request message comprising third ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast thesecond ranging signal in the second ranging session.

33. The responder UE of clause 32, further comprising:

means for performing the first ranging session with the first initiatorUE comprising broadcasting the first ranging signal according to thefirst ranging signal resources; and

means for performing the second ranging session with the secondinitiator UE comprising broadcasting the second ranging signal accordingto the third ranging signal resources.

34. A non-transitory storage medium including program code storedthereon, the program code is operable to configure at least oneprocessor in a responder user equipment for ranging between UEs, theresponder UE the program code comprising instructions to:

receive a first pre-ranging request message from a first initiator UE toinitiate a first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session;

receive a second pre-ranging request message from a second initiator UEto initiate a second ranging session, the second pre-ranging requestmessage comprising second ranging signal resources including a time andfrequencies for the responder UE to broadcast a second ranging signal inthe second ranging session;

determine a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources;

send a first pre-ranging response message to the first initiator UEacknowledging the first pre-ranging request message; and

send a second pre-ranging response message to the second initiator UEindicating the collision with the second ranging signal resources forthe second ranging signal.

35. The non-transitory storage medium including program code of clause34, wherein the program code to determine the collision between thefirst ranging signal and the second ranging signal comprises programcode to determine that the time to broadcast the second ranging signalis within a predetermined amount of time of the time to broadcast thefirst ranging signal.

36. The non-transitory storage medium including program code of clause35, wherein the predetermined amount of time is a predetermined maximumwait time for a listen-before-transmit procedure for broadcasting thesecond ranging signal.

37. The non-transitory storage medium including program code of clause35, wherein the predetermined amount of time is a predeterminedcollision threshold time.

38. The non-transitory storage medium including program code of any ofclauses 35-37, wherein the program code to determine the collisionbetween the first ranging signal and the second ranging signal comprisesprogram code to determine that the frequencies to broadcast the secondranging signal and the frequencies to broadcast the first ranging signalare the same.

39. The non-transitory storage medium including program code of any ofclauses 34-38, further comprising program code to determine an availabletime to broadcast the second ranging signal, wherein the secondpre-ranging response message includes the available time to broadcastthe second ranging signal.

40. The non-transitory storage medium including program code of clause39, wherein the available time to broadcast the second ranging signal isbased on the time to broadcast the first ranging signal included in thefirst ranging signal resources.

41. The non-transitory storage medium including program code of clause40, wherein the available time to broadcast the second ranging signal isfurther based on a predetermined maximum wait time for alisten-before-transmit procedure for broadcasting the first rangingsignal.

42. The non-transitory storage medium including program code of clause40, wherein the available time to broadcast the second ranging signal isfurther based on a predetermined collision threshold time.

43. The non-transitory storage medium including program code of any ofclauses 34-42, further comprising program code to receive a thirdpre-ranging request message from the second initiator UE to initiate thesecond ranging session, the third pre-ranging request message comprisingthird ranging signal resources including a time and frequencies for theresponder UE to broadcast the second ranging signal in the secondranging session.

44. The non-transitory storage medium including program code of clause43, further comprising program code to:

perform the first ranging session with the first initiator UE comprisingbroadcasting the first ranging signal according to the first rangingsignal resources; and

perform the second ranging session with the second initiator UEcomprising broadcasting the second ranging signal according to the thirdranging signal resources.

45. A method of ranging between user equipments (UEs) performed by aninitiator UE, the method comprising:

transmitting a first pre-ranging request message to a responder UE toinitiate a first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; and

receiving a first pre-ranging response message from the responder UEindicating a collision between the first ranging signal resources forthe first ranging signal and second ranging signal resources for asecond ranging signal for a second initiator UE.

46. The method of clause 45, further comprising:

determining an available time for the responder UE to broadcast thefirst ranging signal; and

transmitting a second pre-ranging request message to the responder UE toinitiate the first ranging session, the second pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the first ranging signalin the first ranging session based on the available time.

47. The method of clause 46, wherein the first pre-ranging responsemessage comprises the available time for the responder UE to broadcastthe first ranging signal.

48. The method of any of clauses 46-47, wherein the available time forthe responder UE to broadcast the first ranging signal is based on thetime to broadcast the first ranging signal included in the first rangingsignal resources and a predetermined time period.

49. The method of clause 48, wherein the predetermined time period isbased on a maximum wait time for a listen-before-transmit procedure forbroadcasting the first ranging signal.

50. The method of clause 48, wherein the predetermined time period is apredetermined collision threshold time period.

51. The method of any of clauses 46-50, further comprising:

receiving a second pre-ranging response message from the responder UEacknowledging the second pre-ranging request message; and

performing the first ranging session with responder UE comprisingreceiving the first ranging signal transmitted by the responder UEaccording to the third ranging signal resources.

52. The method of clause 45, further comprising performing the firstranging session with responder UE comprising transmitting an initialranging signal and waiting to receive the first ranging signaltransmitted by the responder UE according to the first ranging signalresources.

53. An initiator user equipment (UE) configured for ranging between UEs,the initiator UE, the method comprising:

a wireless transceiver configured to wirelessly communicate withentities in a wireless network;

at least one memory; and

at least one processor coupled to the wireless transceiver and the atleast one memory, wherein the at least one processor is configured to:

transmit a first pre-ranging request message to a responder UE toinitiate a first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; and

receive a first pre-ranging response message from the responder UEindicating a collision between the first ranging signal resources forthe first ranging signal and second ranging signal resources for asecond ranging signal for a second initiator UE.

54. The initiator UE of clause 53, wherein the at least one processor isfurther configured to:

determine an available time for the responder UE to broadcast the firstranging signal; and

transmit a second pre-ranging request message to the responder UE toinitiate the first ranging session, the second pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the first ranging signalin the first ranging session based on the available time.

55. The initiator UE of clause 54, wherein the first pre-rangingresponse message comprises the available time for the responder UE tobroadcast the first ranging signal.

56. The initiator UE of any of clauses 54-55, wherein the available timefor the responder UE to broadcast the first ranging signal is based onthe time to broadcast the first ranging signal included in the firstranging signal resources and a predetermined time period.

57. The initiator UE of clause 56, wherein the predetermined time periodis based on a maximum wait time for a listen-before-transmit procedurefor broadcasting the first ranging signal.

58. The initiator UE of clause 56, wherein the predetermined time periodis a predetermined collision threshold time period.

59. The initiator UE of any of clauses 54-58, wherein the at least oneprocessor is further configured to:

receive a second pre-ranging response message from the responder UEacknowledging the second pre-ranging request message; and

perform the first ranging session with responder UE comprising receivingthe first ranging signal transmitted by the responder UE according tothe third ranging signal resources.

60. The initiator UE of clause 53, wherein the at least one processor isfurther configured to perform the first ranging session with responderUE by being configured to transmit an initial ranging signal and wait toreceive the first ranging signal transmitted by the responder UEaccording to the first ranging signal resources.

61. An initiator user equipment (UE) configured for ranging between UEs,the initiator UE comprising:

means for transmitting a first pre-ranging request message to aresponder UE to initiate a first ranging session, the first pre-rangingrequest message comprising first ranging signal resources including atime and frequencies for the responder UE to broadcast a first rangingsignal in the first ranging session; and

means for receiving a first pre-ranging response message from theresponder UE indicating a collision between the first ranging signalresources for the first ranging signal and second ranging signalresources for a second ranging signal for a second initiator UE.

62. The initiator UE of clause 61, further comprising:

means for determining an available time for the responder UE tobroadcast the first ranging signal; and

means for transmitting a second pre-ranging request message to theresponder UE to initiate the first ranging session, the secondpre-ranging request message comprising third ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast thefirst ranging signal in the first ranging session based on the availabletime.

63. The initiator UE of clause 62, wherein the first pre-rangingresponse message comprises the available time for the responder UE tobroadcast the first ranging signal.

64. The initiator UE of any of clauses 62-63, wherein the available timefor the responder UE to broadcast the first ranging signal is based onthe time to broadcast the first ranging signal included in the firstranging signal resources and a predetermined time period.

65. The initiator UE of clause 64, wherein the predetermined time periodis based on a maximum wait time for a listen-before-transmit procedurefor broadcasting the first ranging signal.

66. The initiator UE of clause 64, wherein the predetermined time periodis a predetermined collision threshold time period.

67. The initiator UE of any of clauses 62-66, further comprising:

means for receiving a second pre-ranging response message from theresponder UE acknowledging the second pre-ranging request message; and

means for performing the first ranging session with responder UEcomprising receiving the first ranging signal transmitted by theresponder UE according to the third ranging signal resources.

68. The initiator UE of clause 61, further comprising means forperforming the first ranging session with responder UE comprising meansfor transmitting an initial ranging signal and waiting to receive thefirst ranging signal transmitted by the responder UE according to thefirst ranging signal resources.

69. A non-transitory storage medium including program code storedthereon, the program code is operable to configure at least oneprocessor in an initiator user equipment (UE) for ranging between UEs,the initiator UE, the program code comprising instructions to:

transmit a first pre-ranging request message to a responder UE toinitiate a first ranging session, the first pre-ranging request messagecomprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; and

receive a first pre-ranging response message from the responder UEindicating a collision between the first ranging signal resources forthe first ranging signal and second ranging signal resources for asecond ranging signal for a second initiator UE.

70. The non-transitory storage medium including program code of clause69, further comprising program code to:

determine an available time for the responder UE to broadcast the firstranging signal; and

transmit a second pre-ranging request message to the responder UE toinitiate the first ranging session, the second pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the first ranging signalin the first ranging session based on the available time.

71. The non-transitory storage medium including program code of clause70, wherein the first pre-ranging response message comprises theavailable time for the responder UE to broadcast the first rangingsignal.

72. The non-transitory storage medium including program code of any ofclauses 70-71, wherein the available time for the responder UE tobroadcast the first ranging signal is based on the time to broadcast thefirst ranging signal included in the first ranging signal resources anda predetermined time period.

73. The non-transitory storage medium including program code of clause72, wherein the predetermined time period is based on a maximum waittime for a listen-before-transmit procedure for broadcasting the firstranging signal.

74. The non-transitory storage medium including program code of clause72, wherein the predetermined time period is a predetermined collisionthreshold time period.

75. The non-transitory storage medium including program code of any ofclauses 70-74, further comprising program code to:

receive a second pre-ranging response message from the responder UEacknowledging the second pre-ranging request message; and

perform the first ranging session with responder UE comprising receivingthe first ranging signal transmitted by the responder UE according tothe third ranging signal resources.

76. The non-transitory storage medium including program code of clause70, further comprising program code to perform the first ranging sessionwith responder UE comprising program code to transmit an initial rangingsignal and to wait to receive the first ranging signal transmitted bythe responder UE according to the first ranging signal resources.

Therefore, it is intended that claimed subject matter not be limited tothe particular examples disclosed, but that such claimed subject mattermay also include all aspects falling within the scope of appendedclaims, and equivalents thereof.

What is claimed is:
 1. A method of ranging between user equipments (UEs)performed by a responder UE, the method comprising: receiving a firstpre-ranging request message from a first initiator UE to initiate afirst ranging session, the first pre-ranging request message comprisingfirst ranging signal resources including a time and frequencies for theresponder UE to broadcast a first ranging signal in the first rangingsession; receiving a second pre-ranging request message from a secondinitiator UE to initiate a second ranging session, the secondpre-ranging request message comprising second ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast asecond ranging signal in the second ranging session; determining acollision between the first ranging signal and the second ranging signalbased on the first ranging signal resources and the second rangingresources; sending a first pre-ranging response message to the firstinitiator UE acknowledging the first pre-ranging request message; andsending a second pre-ranging response message to the second initiator UEindicating the collision with the second ranging signal resources forthe second ranging signal.
 2. The method of claim 1, wherein determiningthe collision between the first ranging signal and the second rangingsignal comprises determining that the time to broadcast the secondranging signal is within a predetermined amount of time of the time tobroadcast the first ranging signal.
 3. The method of claim 2, whereinthe predetermined amount of time is a predetermined maximum wait timefor a listen-before-transmit procedure for broadcasting the secondranging signal.
 4. The method of claim 2, wherein the predeterminedamount of time is a predetermined collision threshold time.
 5. Themethod of claim 2, wherein determining the collision between the firstranging signal and the second ranging signal comprises determining thatthe frequencies to broadcast the second ranging signal and thefrequencies to broadcast the first ranging signal are the same.
 6. Themethod of claim 1, further comprising determining an available time tobroadcast the second ranging signal, wherein the second pre-rangingresponse message includes the available time to broadcast the secondranging signal.
 7. The method of claim 6, wherein the available time tobroadcast the second ranging signal is based on the time to broadcastthe first ranging signal included in the first ranging signal resources.8. The method of claim 7, wherein the available time to broadcast thesecond ranging signal is further based on a predetermined maximum waittime for a listen-before-transmit procedure for broadcasting the firstranging signal.
 9. The method of claim 7, wherein the available time tobroadcast the second ranging signal is further based on a predeterminedcollision threshold time.
 10. The method of claim 1, further comprisingreceiving a third pre-ranging request message from the second initiatorUE to initiate the second ranging session, the third pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the second ranging signalin the second ranging session.
 11. The method of claim 10, furthercomprising: performing the first ranging session with the firstinitiator UE comprising broadcasting the first ranging signal accordingto the first ranging signal resources; and performing the second rangingsession with the second initiator UE comprising broadcasting the secondranging signal according to the third ranging signal resources.
 12. Aresponder user equipment configured for ranging between UEs, theresponder UE comprising: a wireless transceiver configured to wirelesslycommunicate with entities in a wireless network; at least one memory;and at least one processor coupled to the wireless transceiver and theat least one memory, wherein the at least one processor is configuredto: receive a first pre-ranging request message from a first initiatorUE to initiate a first ranging session, the first pre-ranging requestmessage comprising first ranging signal resources including a time andfrequencies for the responder UE to broadcast a first ranging signal inthe first ranging session; receive a second pre-ranging request messagefrom a second initiator UE to initiate a second ranging session, thesecond pre-ranging request message comprising second ranging signalresources including a time and frequencies for the responder UE tobroadcast a second ranging signal in the second ranging session;determine a collision between the first ranging signal and the secondranging signal based on the first ranging signal resources and thesecond ranging resources; send a first pre-ranging response message tothe first initiator UE acknowledging the first pre-ranging requestmessage; and send a second pre-ranging response message to the secondinitiator UE indicating the collision with the second ranging signalresources for the second ranging signal.
 13. The responder UE of claim12, wherein the at least one processor is configured to determine thecollision between the first ranging signal and the second ranging signalby being configured to determine that the time to broadcast the secondranging signal is within a predetermined amount of time of the time tobroadcast the first ranging signal.
 14. The responder UE of claim 13,wherein the predetermined amount of time is a predetermined maximum waittime for a listen-before-transmit procedure for broadcasting the secondranging signal.
 15. The responder UE of claim 13, wherein thepredetermined amount of time is a predetermined collision thresholdtime.
 16. The responder UE of claim 13, wherein the at least oneprocessor is configured to determine the collision between the firstranging signal and the second ranging signal by being configured todetermine that the frequencies to broadcast the second ranging signaland the frequencies to broadcast the first ranging signal are the same.17. The responder UE of claim 12, wherein the at least one processor isfurther configured to determine an available time to broadcast thesecond ranging signal, wherein the second pre-ranging response messageincludes the available time to broadcast the second ranging signal. 18.The responder UE of claim 17, wherein the available time to broadcastthe second ranging signal is based on the time to broadcast the firstranging signal included in the first ranging signal resources.
 19. Theresponder UE of claim 18, wherein the available time to broadcast thesecond ranging signal is further based on a predetermined maximum waittime for a listen-before-transmit procedure for broadcasting the firstranging signal.
 20. The responder UE of claim 18, wherein the availabletime to broadcast the second ranging signal is further based on apredetermined collision threshold time.
 21. The responder UE of claim12, wherein the at least one processor is further configured to receivea third pre-ranging request message from the second initiator UE toinitiate the second ranging session, the third pre-ranging requestmessage comprising third ranging signal resources including a time andfrequencies for the responder UE to broadcast the second ranging signalin the second ranging session.
 22. The responder UE of claim 21, whereinthe at least one processor is further configured to: perform the firstranging session with the first initiator UE by being configured tobroadcast the first ranging signal according to the first ranging signalresources; and perform the second ranging session with the secondinitiator UE by being configured to broadcast the second ranging signalaccording to the third ranging signal resources.
 23. A responder userequipment configured for ranging between UEs, the responder UEcomprising: means for receiving a first pre-ranging request message froma first initiator UE to initiate a first ranging session, the firstpre-ranging request message comprising first ranging signal resourcesincluding a time and frequencies for the responder UE to broadcast afirst ranging signal in the first ranging session; means for receiving asecond pre-ranging request message from a second initiator UE toinitiate a second ranging session, the second pre-ranging requestmessage comprising second ranging signal resources including a time andfrequencies for the responder UE to broadcast a second ranging signal inthe second ranging session; means for determining a collision betweenthe first ranging signal and the second ranging signal based on thefirst ranging signal resources and the second ranging resources; meansfor sending a first pre-ranging response message to the first initiatorUE acknowledging the first pre-ranging request message; and means forsending a second pre-ranging response message to the second initiator UEindicating the collision with the second ranging signal resources forthe second ranging signal.
 24. The responder UE of claim 23, wherein themeans for determining the collision between the first ranging signal andthe second ranging signal comprises means for determining that the timeto broadcast the second ranging signal is within a predetermined amountof time of the time to broadcast the first ranging signal, wherein thepredetermined amount of time is a predetermined maximum wait time for alisten-before-transmit procedure for broadcasting the second rangingsignal or a predetermined collision threshold time.
 25. The responder UEof claim 24, wherein means for determining the collision between thefirst ranging signal and the second ranging signal comprises means fordetermining that the frequencies to broadcast the second ranging signaland the frequencies to broadcast the first ranging signal are the same.26. The responder UE of claim 23, further comprising means fordetermining an available time to broadcast the second ranging signal,wherein the second pre-ranging response message includes the availabletime to broadcast the second ranging signal.
 27. The responder UE ofclaim 26, wherein the available time to broadcast the second rangingsignal is based on the time to broadcast the first ranging signalincluded in the first ranging signal resources.
 28. The responder UE ofclaim 27, wherein the available time to broadcast the second rangingsignal is further based on a predetermined maximum wait time for alisten-before-transmit procedure for broadcasting the first rangingsignal.
 29. The responder UE of claim 27, wherein the available time tobroadcast the second ranging signal is further based on a predeterminedcollision threshold time.
 30. The responder UE of claim 23, furthercomprising means for receiving a third pre-ranging request message fromthe second initiator UE to initiate the second ranging session, thethird pre-ranging request message comprising third ranging signalresources including a time and frequencies for the responder UE tobroadcast the second ranging signal in the second ranging session. 31.The responder UE of claim 30, further comprising: means for performingthe first ranging session with the first initiator UE comprisingbroadcasting the first ranging signal according to the first rangingsignal resources; and means for performing the second ranging sessionwith the second initiator UE comprising broadcasting the second rangingsignal according to the third ranging signal resources.